Merge tag 'f2fs-for-5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeu...

[platform/kernel/linux-starfive.git] / mm / mmap.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * mm/mmap.c
 *
 * Written by obz.
 *
 * Address space accounting code        <alan@lxorguk.ukuu.org.uk>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/mm.h>
#include <linux/vmacache.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/capability.h>
#include <linux/init.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/hugetlb.h>
#include <linux/shmem_fs.h>
#include <linux/profile.h>
#include <linux/export.h>
#include <linux/mount.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>
#include <linux/mmu_notifier.h>
#include <linux/mmdebug.h>
#include <linux/perf_event.h>
#include <linux/audit.h>
#include <linux/khugepaged.h>
#include <linux/uprobes.h>
#include <linux/rbtree_augmented.h>
#include <linux/notifier.h>
#include <linux/memory.h>
#include <linux/printk.h>
#include <linux/userfaultfd_k.h>
#include <linux/moduleparam.h>
#include <linux/pkeys.h>
#include <linux/oom.h>
#include <linux/sched/mm.h>

#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/tlb.h>
#include <asm/mmu_context.h>

#define CREATE_TRACE_POINTS
#include <trace/events/mmap.h>

#include "internal.h"

#ifndef arch_mmap_check
#define arch_mmap_check(addr, len, flags)       (0)
#endif

#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
const int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
const int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX;
int mmap_rnd_bits __read_mostly = CONFIG_ARCH_MMAP_RND_BITS;
#endif
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
const int mmap_rnd_compat_bits_min = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN;
const int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
int mmap_rnd_compat_bits __read_mostly = CONFIG_ARCH_MMAP_RND_COMPAT_BITS;
#endif

static bool ignore_rlimit_data;
core_param(ignore_rlimit_data, ignore_rlimit_data, bool, 0644);

static void unmap_region(struct mm_struct *mm,
                struct vm_area_struct *vma, struct vm_area_struct *prev,
                unsigned long start, unsigned long end);

/* description of effects of mapping type and prot in current implementation.
 * this is due to the limited x86 page protection hardware.  The expected
 * behavior is in parens:
 *
 * map_type     prot
 *              PROT_NONE       PROT_READ       PROT_WRITE      PROT_EXEC
 * MAP_SHARED   r: (no) no      r: (yes) yes    r: (no) yes     r: (no) yes
 *              w: (no) no      w: (no) no      w: (yes) yes    w: (no) no
 *              x: (no) no      x: (no) yes     x: (no) yes     x: (yes) yes
 *
 * MAP_PRIVATE  r: (no) no      r: (yes) yes    r: (no) yes     r: (no) yes
 *              w: (no) no      w: (no) no      w: (copy) copy  w: (no) no
 *              x: (no) no      x: (no) yes     x: (no) yes     x: (yes) yes
 *
 * On arm64, PROT_EXEC has the following behaviour for both MAP_SHARED and
 * MAP_PRIVATE (with Enhanced PAN supported):
 *                                                              r: (no) no
 *                                                              w: (no) no
 *                                                              x: (yes) yes
 */
pgprot_t protection_map[16] __ro_after_init = {
        __P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
        __S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
};

#ifndef CONFIG_ARCH_HAS_FILTER_PGPROT
static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
{
        return prot;
}
#endif

pgprot_t vm_get_page_prot(unsigned long vm_flags)
{
        pgprot_t ret = __pgprot(pgprot_val(protection_map[vm_flags &
                                (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
                        pgprot_val(arch_vm_get_page_prot(vm_flags)));

        return arch_filter_pgprot(ret);
}
EXPORT_SYMBOL(vm_get_page_prot);

static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
{
        return pgprot_modify(oldprot, vm_get_page_prot(vm_flags));
}

/* Update vma->vm_page_prot to reflect vma->vm_flags. */
void vma_set_page_prot(struct vm_area_struct *vma)
{
        unsigned long vm_flags = vma->vm_flags;
        pgprot_t vm_page_prot;

        vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
        if (vma_wants_writenotify(vma, vm_page_prot)) {
                vm_flags &= ~VM_SHARED;
                vm_page_prot = vm_pgprot_modify(vm_page_prot, vm_flags);
        }
        /* remove_protection_ptes reads vma->vm_page_prot without mmap_lock */
        WRITE_ONCE(vma->vm_page_prot, vm_page_prot);
}

/*
 * Requires inode->i_mapping->i_mmap_rwsem
 */
static void __remove_shared_vm_struct(struct vm_area_struct *vma,
                struct file *file, struct address_space *mapping)
{
        if (vma->vm_flags & VM_DENYWRITE)
                allow_write_access(file);
        if (vma->vm_flags & VM_SHARED)
                mapping_unmap_writable(mapping);

        flush_dcache_mmap_lock(mapping);
        vma_interval_tree_remove(vma, &mapping->i_mmap);
        flush_dcache_mmap_unlock(mapping);
}

/*
 * Unlink a file-based vm structure from its interval tree, to hide
 * vma from rmap and vmtruncate before freeing its page tables.
 */
void unlink_file_vma(struct vm_area_struct *vma)
{
        struct file *file = vma->vm_file;

        if (file) {
                struct address_space *mapping = file->f_mapping;
                i_mmap_lock_write(mapping);
                __remove_shared_vm_struct(vma, file, mapping);
                i_mmap_unlock_write(mapping);
        }
}

/*
 * Close a vm structure and free it, returning the next.
 */
static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
{
        struct vm_area_struct *next = vma->vm_next;

        might_sleep();
        if (vma->vm_ops && vma->vm_ops->close)
                vma->vm_ops->close(vma);
        if (vma->vm_file)
                fput(vma->vm_file);
        mpol_put(vma_policy(vma));
        vm_area_free(vma);
        return next;
}

static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long flags,
                struct list_head *uf);
SYSCALL_DEFINE1(brk, unsigned long, brk)
{
        unsigned long newbrk, oldbrk, origbrk;
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *next;
        unsigned long min_brk;
        bool populate;
        bool downgraded = false;
        LIST_HEAD(uf);

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        origbrk = mm->brk;

#ifdef CONFIG_COMPAT_BRK
        /*
         * CONFIG_COMPAT_BRK can still be overridden by setting
         * randomize_va_space to 2, which will still cause mm->start_brk
         * to be arbitrarily shifted
         */
        if (current->brk_randomized)
                min_brk = mm->start_brk;
        else
                min_brk = mm->end_data;
#else
        min_brk = mm->start_brk;
#endif
        if (brk < min_brk)
                goto out;

        /*
         * Check against rlimit here. If this check is done later after the test
         * of oldbrk with newbrk then it can escape the test and let the data
         * segment grow beyond its set limit the in case where the limit is
         * not page aligned -Ram Gupta
         */
        if (check_data_rlimit(rlimit(RLIMIT_DATA), brk, mm->start_brk,
                              mm->end_data, mm->start_data))
                goto out;

        newbrk = PAGE_ALIGN(brk);
        oldbrk = PAGE_ALIGN(mm->brk);
        if (oldbrk == newbrk) {
                mm->brk = brk;
                goto success;
        }

        /*
         * Always allow shrinking brk.
         * __do_munmap() may downgrade mmap_lock to read.
         */
        if (brk <= mm->brk) {
                int ret;

                /*
                 * mm->brk must to be protected by write mmap_lock so update it
                 * before downgrading mmap_lock. When __do_munmap() fails,
                 * mm->brk will be restored from origbrk.
                 */
                mm->brk = brk;
                ret = __do_munmap(mm, newbrk, oldbrk-newbrk, &uf, true);
                if (ret < 0) {
                        mm->brk = origbrk;
                        goto out;
                } else if (ret == 1) {
                        downgraded = true;
                }
                goto success;
        }

        /* Check against existing mmap mappings. */
        next = find_vma(mm, oldbrk);
        if (next && newbrk + PAGE_SIZE > vm_start_gap(next))
                goto out;

        /* Ok, looks good - let it rip. */
        if (do_brk_flags(oldbrk, newbrk-oldbrk, 0, &uf) < 0)
                goto out;
        mm->brk = brk;

success:
        populate = newbrk > oldbrk && (mm->def_flags & VM_LOCKED) != 0;
        if (downgraded)
                mmap_read_unlock(mm);
        else
                mmap_write_unlock(mm);
        userfaultfd_unmap_complete(mm, &uf);
        if (populate)
                mm_populate(oldbrk, newbrk - oldbrk);
        return brk;

out:
        mmap_write_unlock(mm);
        return origbrk;
}

static inline unsigned long vma_compute_gap(struct vm_area_struct *vma)
{
        unsigned long gap, prev_end;

        /*
         * Note: in the rare case of a VM_GROWSDOWN above a VM_GROWSUP, we
         * allow two stack_guard_gaps between them here, and when choosing
         * an unmapped area; whereas when expanding we only require one.
         * That's a little inconsistent, but keeps the code here simpler.
         */
        gap = vm_start_gap(vma);
        if (vma->vm_prev) {
                prev_end = vm_end_gap(vma->vm_prev);
                if (gap > prev_end)
                        gap -= prev_end;
                else
                        gap = 0;
        }
        return gap;
}

#ifdef CONFIG_DEBUG_VM_RB
static unsigned long vma_compute_subtree_gap(struct vm_area_struct *vma)
{
        unsigned long max = vma_compute_gap(vma), subtree_gap;
        if (vma->vm_rb.rb_left) {
                subtree_gap = rb_entry(vma->vm_rb.rb_left,
                                struct vm_area_struct, vm_rb)->rb_subtree_gap;
                if (subtree_gap > max)
                        max = subtree_gap;
        }
        if (vma->vm_rb.rb_right) {
                subtree_gap = rb_entry(vma->vm_rb.rb_right,
                                struct vm_area_struct, vm_rb)->rb_subtree_gap;
                if (subtree_gap > max)
                        max = subtree_gap;
        }
        return max;
}

static int browse_rb(struct mm_struct *mm)
{
        struct rb_root *root = &mm->mm_rb;
        int i = 0, j, bug = 0;
        struct rb_node *nd, *pn = NULL;
        unsigned long prev = 0, pend = 0;

        for (nd = rb_first(root); nd; nd = rb_next(nd)) {
                struct vm_area_struct *vma;
                vma = rb_entry(nd, struct vm_area_struct, vm_rb);
                if (vma->vm_start < prev) {
                        pr_emerg("vm_start %lx < prev %lx\n",
                                  vma->vm_start, prev);
                        bug = 1;
                }
                if (vma->vm_start < pend) {
                        pr_emerg("vm_start %lx < pend %lx\n",
                                  vma->vm_start, pend);
                        bug = 1;
                }
                if (vma->vm_start > vma->vm_end) {
                        pr_emerg("vm_start %lx > vm_end %lx\n",
                                  vma->vm_start, vma->vm_end);
                        bug = 1;
                }
                spin_lock(&mm->page_table_lock);
                if (vma->rb_subtree_gap != vma_compute_subtree_gap(vma)) {
                        pr_emerg("free gap %lx, correct %lx\n",
                               vma->rb_subtree_gap,
                               vma_compute_subtree_gap(vma));
                        bug = 1;
                }
                spin_unlock(&mm->page_table_lock);
                i++;
                pn = nd;
                prev = vma->vm_start;
                pend = vma->vm_end;
        }
        j = 0;
        for (nd = pn; nd; nd = rb_prev(nd))
                j++;
        if (i != j) {
                pr_emerg("backwards %d, forwards %d\n", j, i);
                bug = 1;
        }
        return bug ? -1 : i;
}

static void validate_mm_rb(struct rb_root *root, struct vm_area_struct *ignore)
{
        struct rb_node *nd;

        for (nd = rb_first(root); nd; nd = rb_next(nd)) {
                struct vm_area_struct *vma;
                vma = rb_entry(nd, struct vm_area_struct, vm_rb);
                VM_BUG_ON_VMA(vma != ignore &&
                        vma->rb_subtree_gap != vma_compute_subtree_gap(vma),
                        vma);
        }
}

static void validate_mm(struct mm_struct *mm)
{
        int bug = 0;
        int i = 0;
        unsigned long highest_address = 0;
        struct vm_area_struct *vma = mm->mmap;

        while (vma) {
                struct anon_vma *anon_vma = vma->anon_vma;
                struct anon_vma_chain *avc;

                if (anon_vma) {
                        anon_vma_lock_read(anon_vma);
                        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                                anon_vma_interval_tree_verify(avc);
                        anon_vma_unlock_read(anon_vma);
                }

                highest_address = vm_end_gap(vma);
                vma = vma->vm_next;
                i++;
        }
        if (i != mm->map_count) {
                pr_emerg("map_count %d vm_next %d\n", mm->map_count, i);
                bug = 1;
        }
        if (highest_address != mm->highest_vm_end) {
                pr_emerg("mm->highest_vm_end %lx, found %lx\n",
                          mm->highest_vm_end, highest_address);
                bug = 1;
        }
        i = browse_rb(mm);
        if (i != mm->map_count) {
                if (i != -1)
                        pr_emerg("map_count %d rb %d\n", mm->map_count, i);
                bug = 1;
        }
        VM_BUG_ON_MM(bug, mm);
}
#else
#define validate_mm_rb(root, ignore) do { } while (0)
#define validate_mm(mm) do { } while (0)
#endif

RB_DECLARE_CALLBACKS_MAX(static, vma_gap_callbacks,
                         struct vm_area_struct, vm_rb,
                         unsigned long, rb_subtree_gap, vma_compute_gap)

/*
 * Update augmented rbtree rb_subtree_gap values after vma->vm_start or
 * vma->vm_prev->vm_end values changed, without modifying the vma's position
 * in the rbtree.
 */
static void vma_gap_update(struct vm_area_struct *vma)
{
        /*
         * As it turns out, RB_DECLARE_CALLBACKS_MAX() already created
         * a callback function that does exactly what we want.
         */
        vma_gap_callbacks_propagate(&vma->vm_rb, NULL);
}

static inline void vma_rb_insert(struct vm_area_struct *vma,
                                 struct rb_root *root)
{
        /* All rb_subtree_gap values must be consistent prior to insertion */
        validate_mm_rb(root, NULL);

        rb_insert_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
}

static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
{
        /*
         * Note rb_erase_augmented is a fairly large inline function,
         * so make sure we instantiate it only once with our desired
         * augmented rbtree callbacks.
         */
        rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
}

static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma,
                                                struct rb_root *root,
                                                struct vm_area_struct *ignore)
{
        /*
         * All rb_subtree_gap values must be consistent prior to erase,
         * with the possible exception of
         *
         * a. the "next" vma being erased if next->vm_start was reduced in
         *    __vma_adjust() -> __vma_unlink()
         * b. the vma being erased in detach_vmas_to_be_unmapped() ->
         *    vma_rb_erase()
         */
        validate_mm_rb(root, ignore);

        __vma_rb_erase(vma, root);
}

static __always_inline void vma_rb_erase(struct vm_area_struct *vma,
                                         struct rb_root *root)
{
        vma_rb_erase_ignore(vma, root, vma);
}

/*
 * vma has some anon_vma assigned, and is already inserted on that
 * anon_vma's interval trees.
 *
 * Before updating the vma's vm_start / vm_end / vm_pgoff fields, the
 * vma must be removed from the anon_vma's interval trees using
 * anon_vma_interval_tree_pre_update_vma().
 *
 * After the update, the vma will be reinserted using
 * anon_vma_interval_tree_post_update_vma().
 *
 * The entire update must be protected by exclusive mmap_lock and by
 * the root anon_vma's mutex.
 */
static inline void
anon_vma_interval_tree_pre_update_vma(struct vm_area_struct *vma)
{
        struct anon_vma_chain *avc;

        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                anon_vma_interval_tree_remove(avc, &avc->anon_vma->rb_root);
}

static inline void
anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
{
        struct anon_vma_chain *avc;

        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root);
}

static int find_vma_links(struct mm_struct *mm, unsigned long addr,
                unsigned long end, struct vm_area_struct **pprev,
                struct rb_node ***rb_link, struct rb_node **rb_parent)
{
        struct rb_node **__rb_link, *__rb_parent, *rb_prev;

        mmap_assert_locked(mm);
        __rb_link = &mm->mm_rb.rb_node;
        rb_prev = __rb_parent = NULL;

        while (*__rb_link) {
                struct vm_area_struct *vma_tmp;

                __rb_parent = *__rb_link;
                vma_tmp = rb_entry(__rb_parent, struct vm_area_struct, vm_rb);

                if (vma_tmp->vm_end > addr) {
                        /* Fail if an existing vma overlaps the area */
                        if (vma_tmp->vm_start < end)
                                return -ENOMEM;
                        __rb_link = &__rb_parent->rb_left;
                } else {
                        rb_prev = __rb_parent;
                        __rb_link = &__rb_parent->rb_right;
                }
        }

        *pprev = NULL;
        if (rb_prev)
                *pprev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
        *rb_link = __rb_link;
        *rb_parent = __rb_parent;
        return 0;
}

/*
 * vma_next() - Get the next VMA.
 * @mm: The mm_struct.
 * @vma: The current vma.
 *
 * If @vma is NULL, return the first vma in the mm.
 *
 * Returns: The next VMA after @vma.
 */
static inline struct vm_area_struct *vma_next(struct mm_struct *mm,
                                         struct vm_area_struct *vma)
{
        if (!vma)
                return mm->mmap;

        return vma->vm_next;
}

/*
 * munmap_vma_range() - munmap VMAs that overlap a range.
 * @mm: The mm struct
 * @start: The start of the range.
 * @len: The length of the range.
 * @pprev: pointer to the pointer that will be set to previous vm_area_struct
 * @rb_link: the rb_node
 * @rb_parent: the parent rb_node
 *
 * Find all the vm_area_struct that overlap from @start to
 * @end and munmap them.  Set @pprev to the previous vm_area_struct.
 *
 * Returns: -ENOMEM on munmap failure or 0 on success.
 */
static inline int
munmap_vma_range(struct mm_struct *mm, unsigned long start, unsigned long len,
                 struct vm_area_struct **pprev, struct rb_node ***link,
                 struct rb_node **parent, struct list_head *uf)
{

        while (find_vma_links(mm, start, start + len, pprev, link, parent))
                if (do_munmap(mm, start, len, uf))
                        return -ENOMEM;

        return 0;
}
static unsigned long count_vma_pages_range(struct mm_struct *mm,
                unsigned long addr, unsigned long end)
{
        unsigned long nr_pages = 0;
        struct vm_area_struct *vma;

        /* Find first overlapping mapping */
        vma = find_vma_intersection(mm, addr, end);
        if (!vma)
                return 0;

        nr_pages = (min(end, vma->vm_end) -
                max(addr, vma->vm_start)) >> PAGE_SHIFT;

        /* Iterate over the rest of the overlaps */
        for (vma = vma->vm_next; vma; vma = vma->vm_next) {
                unsigned long overlap_len;

                if (vma->vm_start > end)
                        break;

                overlap_len = min(end, vma->vm_end) - vma->vm_start;
                nr_pages += overlap_len >> PAGE_SHIFT;
        }

        return nr_pages;
}

void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
                struct rb_node **rb_link, struct rb_node *rb_parent)
{
        /* Update tracking information for the gap following the new vma. */
        if (vma->vm_next)
                vma_gap_update(vma->vm_next);
        else
                mm->highest_vm_end = vm_end_gap(vma);

        /*
         * vma->vm_prev wasn't known when we followed the rbtree to find the
         * correct insertion point for that vma. As a result, we could not
         * update the vma vm_rb parents rb_subtree_gap values on the way down.
         * So, we first insert the vma with a zero rb_subtree_gap value
         * (to be consistent with what we did on the way down), and then
         * immediately update the gap to the correct value. Finally we
         * rebalance the rbtree after all augmented values have been set.
         */
        rb_link_node(&vma->vm_rb, rb_parent, rb_link);
        vma->rb_subtree_gap = 0;
        vma_gap_update(vma);
        vma_rb_insert(vma, &mm->mm_rb);
}

static void __vma_link_file(struct vm_area_struct *vma)
{
        struct file *file;

        file = vma->vm_file;
        if (file) {
                struct address_space *mapping = file->f_mapping;

                if (vma->vm_flags & VM_DENYWRITE)
                        put_write_access(file_inode(file));
                if (vma->vm_flags & VM_SHARED)
                        mapping_allow_writable(mapping);

                flush_dcache_mmap_lock(mapping);
                vma_interval_tree_insert(vma, &mapping->i_mmap);
                flush_dcache_mmap_unlock(mapping);
        }
}

static void
__vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
        struct vm_area_struct *prev, struct rb_node **rb_link,
        struct rb_node *rb_parent)
{
        __vma_link_list(mm, vma, prev);
        __vma_link_rb(mm, vma, rb_link, rb_parent);
}

static void vma_link(struct mm_struct *mm, struct vm_area_struct *vma,
                        struct vm_area_struct *prev, struct rb_node **rb_link,
                        struct rb_node *rb_parent)
{
        struct address_space *mapping = NULL;

        if (vma->vm_file) {
                mapping = vma->vm_file->f_mapping;
                i_mmap_lock_write(mapping);
        }

        __vma_link(mm, vma, prev, rb_link, rb_parent);
        __vma_link_file(vma);

        if (mapping)
                i_mmap_unlock_write(mapping);

        mm->map_count++;
        validate_mm(mm);
}

/*
 * Helper for vma_adjust() in the split_vma insert case: insert a vma into the
 * mm's list and rbtree.  It has already been inserted into the interval tree.
 */
static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
{
        struct vm_area_struct *prev;
        struct rb_node **rb_link, *rb_parent;

        if (find_vma_links(mm, vma->vm_start, vma->vm_end,
                           &prev, &rb_link, &rb_parent))
                BUG();
        __vma_link(mm, vma, prev, rb_link, rb_parent);
        mm->map_count++;
}

static __always_inline void __vma_unlink(struct mm_struct *mm,
                                                struct vm_area_struct *vma,
                                                struct vm_area_struct *ignore)
{
        vma_rb_erase_ignore(vma, &mm->mm_rb, ignore);
        __vma_unlink_list(mm, vma);
        /* Kill the cache */
        vmacache_invalidate(mm);
}

/*
 * We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
 * is already present in an i_mmap tree without adjusting the tree.
 * The following helper function should be used when such adjustments
 * are necessary.  The "insert" vma (if any) is to be inserted
 * before we drop the necessary locks.
 */
int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
        unsigned long end, pgoff_t pgoff, struct vm_area_struct *insert,
        struct vm_area_struct *expand)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *next = vma->vm_next, *orig_vma = vma;
        struct address_space *mapping = NULL;
        struct rb_root_cached *root = NULL;
        struct anon_vma *anon_vma = NULL;
        struct file *file = vma->vm_file;
        bool start_changed = false, end_changed = false;
        long adjust_next = 0;
        int remove_next = 0;

        if (next && !insert) {
                struct vm_area_struct *exporter = NULL, *importer = NULL;

                if (end >= next->vm_end) {
                        /*
                         * vma expands, overlapping all the next, and
                         * perhaps the one after too (mprotect case 6).
                         * The only other cases that gets here are
                         * case 1, case 7 and case 8.
                         */
                        if (next == expand) {
                                /*
                                 * The only case where we don't expand "vma"
                                 * and we expand "next" instead is case 8.
                                 */
                                VM_WARN_ON(end != next->vm_end);
                                /*
                                 * remove_next == 3 means we're
                                 * removing "vma" and that to do so we
                                 * swapped "vma" and "next".
                                 */
                                remove_next = 3;
                                VM_WARN_ON(file != next->vm_file);
                                swap(vma, next);
                        } else {
                                VM_WARN_ON(expand != vma);
                                /*
                                 * case 1, 6, 7, remove_next == 2 is case 6,
                                 * remove_next == 1 is case 1 or 7.
                                 */
                                remove_next = 1 + (end > next->vm_end);
                                VM_WARN_ON(remove_next == 2 &&
                                           end != next->vm_next->vm_end);
                                /* trim end to next, for case 6 first pass */
                                end = next->vm_end;
                        }

                        exporter = next;
                        importer = vma;

                        /*
                         * If next doesn't have anon_vma, import from vma after
                         * next, if the vma overlaps with it.
                         */
                        if (remove_next == 2 && !next->anon_vma)
                                exporter = next->vm_next;

                } else if (end > next->vm_start) {
                        /*
                         * vma expands, overlapping part of the next:
                         * mprotect case 5 shifting the boundary up.
                         */
                        adjust_next = (end - next->vm_start);
                        exporter = next;
                        importer = vma;
                        VM_WARN_ON(expand != importer);
                } else if (end < vma->vm_end) {
                        /*
                         * vma shrinks, and !insert tells it's not
                         * split_vma inserting another: so it must be
                         * mprotect case 4 shifting the boundary down.
                         */
                        adjust_next = -(vma->vm_end - end);
                        exporter = vma;
                        importer = next;
                        VM_WARN_ON(expand != importer);
                }

                /*
                 * Easily overlooked: when mprotect shifts the boundary,
                 * make sure the expanding vma has anon_vma set if the
                 * shrinking vma had, to cover any anon pages imported.
                 */
                if (exporter && exporter->anon_vma && !importer->anon_vma) {
                        int error;

                        importer->anon_vma = exporter->anon_vma;
                        error = anon_vma_clone(importer, exporter);
                        if (error)
                                return error;
                }
        }
again:
        vma_adjust_trans_huge(orig_vma, start, end, adjust_next);

        if (file) {
                mapping = file->f_mapping;
                root = &mapping->i_mmap;
                uprobe_munmap(vma, vma->vm_start, vma->vm_end);

                if (adjust_next)
                        uprobe_munmap(next, next->vm_start, next->vm_end);

                i_mmap_lock_write(mapping);
                if (insert) {
                        /*
                         * Put into interval tree now, so instantiated pages
                         * are visible to arm/parisc __flush_dcache_page
                         * throughout; but we cannot insert into address
                         * space until vma start or end is updated.
                         */
                        __vma_link_file(insert);
                }
        }

        anon_vma = vma->anon_vma;
        if (!anon_vma && adjust_next)
                anon_vma = next->anon_vma;
        if (anon_vma) {
                VM_WARN_ON(adjust_next && next->anon_vma &&
                           anon_vma != next->anon_vma);
                anon_vma_lock_write(anon_vma);
                anon_vma_interval_tree_pre_update_vma(vma);
                if (adjust_next)
                        anon_vma_interval_tree_pre_update_vma(next);
        }

        if (file) {
                flush_dcache_mmap_lock(mapping);
                vma_interval_tree_remove(vma, root);
                if (adjust_next)
                        vma_interval_tree_remove(next, root);
        }

        if (start != vma->vm_start) {
                vma->vm_start = start;
                start_changed = true;
        }
        if (end != vma->vm_end) {
                vma->vm_end = end;
                end_changed = true;
        }
        vma->vm_pgoff = pgoff;
        if (adjust_next) {
                next->vm_start += adjust_next;
                next->vm_pgoff += adjust_next >> PAGE_SHIFT;
        }

        if (file) {
                if (adjust_next)
                        vma_interval_tree_insert(next, root);
                vma_interval_tree_insert(vma, root);
                flush_dcache_mmap_unlock(mapping);
        }

        if (remove_next) {
                /*
                 * vma_merge has merged next into vma, and needs
                 * us to remove next before dropping the locks.
                 */
                if (remove_next != 3)
                        __vma_unlink(mm, next, next);
                else
                        /*
                         * vma is not before next if they've been
                         * swapped.
                         *
                         * pre-swap() next->vm_start was reduced so
                         * tell validate_mm_rb to ignore pre-swap()
                         * "next" (which is stored in post-swap()
                         * "vma").
                         */
                        __vma_unlink(mm, next, vma);
                if (file)
                        __remove_shared_vm_struct(next, file, mapping);
        } else if (insert) {
                /*
                 * split_vma has split insert from vma, and needs
                 * us to insert it before dropping the locks
                 * (it may either follow vma or precede it).
                 */
                __insert_vm_struct(mm, insert);
        } else {
                if (start_changed)
                        vma_gap_update(vma);
                if (end_changed) {
                        if (!next)
                                mm->highest_vm_end = vm_end_gap(vma);
                        else if (!adjust_next)
                                vma_gap_update(next);
                }
        }

        if (anon_vma) {
                anon_vma_interval_tree_post_update_vma(vma);
                if (adjust_next)
                        anon_vma_interval_tree_post_update_vma(next);
                anon_vma_unlock_write(anon_vma);
        }

        if (file) {
                i_mmap_unlock_write(mapping);
                uprobe_mmap(vma);

                if (adjust_next)
                        uprobe_mmap(next);
        }

        if (remove_next) {
                if (file) {
                        uprobe_munmap(next, next->vm_start, next->vm_end);
                        fput(file);
                }
                if (next->anon_vma)
                        anon_vma_merge(vma, next);
                mm->map_count--;
                mpol_put(vma_policy(next));
                vm_area_free(next);
                /*
                 * In mprotect's case 6 (see comments on vma_merge),
                 * we must remove another next too. It would clutter
                 * up the code too much to do both in one go.
                 */
                if (remove_next != 3) {
                        /*
                         * If "next" was removed and vma->vm_end was
                         * expanded (up) over it, in turn
                         * "next->vm_prev->vm_end" changed and the
                         * "vma->vm_next" gap must be updated.
                         */
                        next = vma->vm_next;
                } else {
                        /*
                         * For the scope of the comment "next" and
                         * "vma" considered pre-swap(): if "vma" was
                         * removed, next->vm_start was expanded (down)
                         * over it and the "next" gap must be updated.
                         * Because of the swap() the post-swap() "vma"
                         * actually points to pre-swap() "next"
                         * (post-swap() "next" as opposed is now a
                         * dangling pointer).
                         */
                        next = vma;
                }
                if (remove_next == 2) {
                        remove_next = 1;
                        end = next->vm_end;
                        goto again;
                }
                else if (next)
                        vma_gap_update(next);
                else {
                        /*
                         * If remove_next == 2 we obviously can't
                         * reach this path.
                         *
                         * If remove_next == 3 we can't reach this
                         * path because pre-swap() next is always not
                         * NULL. pre-swap() "next" is not being
                         * removed and its next->vm_end is not altered
                         * (and furthermore "end" already matches
                         * next->vm_end in remove_next == 3).
                         *
                         * We reach this only in the remove_next == 1
                         * case if the "next" vma that was removed was
                         * the highest vma of the mm. However in such
                         * case next->vm_end == "end" and the extended
                         * "vma" has vma->vm_end == next->vm_end so
                         * mm->highest_vm_end doesn't need any update
                         * in remove_next == 1 case.
                         */
                        VM_WARN_ON(mm->highest_vm_end != vm_end_gap(vma));
                }
        }
        if (insert && file)
                uprobe_mmap(insert);

        validate_mm(mm);

        return 0;
}

/*
 * If the vma has a ->close operation then the driver probably needs to release
 * per-vma resources, so we don't attempt to merge those.
 */
static inline int is_mergeable_vma(struct vm_area_struct *vma,
                                struct file *file, unsigned long vm_flags,
                                struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
{
        /*
         * VM_SOFTDIRTY should not prevent from VMA merging, if we
         * match the flags but dirty bit -- the caller should mark
         * merged VMA as dirty. If dirty bit won't be excluded from
         * comparison, we increase pressure on the memory system forcing
         * the kernel to generate new VMAs when old one could be
         * extended instead.
         */
        if ((vma->vm_flags ^ vm_flags) & ~VM_SOFTDIRTY)
                return 0;
        if (vma->vm_file != file)
                return 0;
        if (vma->vm_ops && vma->vm_ops->close)
                return 0;
        if (!is_mergeable_vm_userfaultfd_ctx(vma, vm_userfaultfd_ctx))
                return 0;
        return 1;
}

static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
                                        struct anon_vma *anon_vma2,
                                        struct vm_area_struct *vma)
{
        /*
         * The list_is_singular() test is to avoid merging VMA cloned from
         * parents. This can improve scalability caused by anon_vma lock.
         */
        if ((!anon_vma1 || !anon_vma2) && (!vma ||
                list_is_singular(&vma->anon_vma_chain)))
                return 1;
        return anon_vma1 == anon_vma2;
}

/*
 * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
 * in front of (at a lower virtual address and file offset than) the vma.
 *
 * We cannot merge two vmas if they have differently assigned (non-NULL)
 * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
 *
 * We don't check here for the merged mmap wrapping around the end of pagecache
 * indices (16TB on ia32) because do_mmap() does not permit mmap's which
 * wrap, nor mmaps which cover the final page at index -1UL.
 */
static int
can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
                     struct anon_vma *anon_vma, struct file *file,
                     pgoff_t vm_pgoff,
                     struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
{
        if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
            is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
                if (vma->vm_pgoff == vm_pgoff)
                        return 1;
        }
        return 0;
}

/*
 * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
 * beyond (at a higher virtual address and file offset than) the vma.
 *
 * We cannot merge two vmas if they have differently assigned (non-NULL)
 * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
 */
static int
can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
                    struct anon_vma *anon_vma, struct file *file,
                    pgoff_t vm_pgoff,
                    struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
{
        if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx) &&
            is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
                pgoff_t vm_pglen;
                vm_pglen = vma_pages(vma);
                if (vma->vm_pgoff + vm_pglen == vm_pgoff)
                        return 1;
        }
        return 0;
}

/*
 * Given a mapping request (addr,end,vm_flags,file,pgoff), figure out
 * whether that can be merged with its predecessor or its successor.
 * Or both (it neatly fills a hole).
 *
 * In most cases - when called for mmap, brk or mremap - [addr,end) is
 * certain not to be mapped by the time vma_merge is called; but when
 * called for mprotect, it is certain to be already mapped (either at
 * an offset within prev, or at the start of next), and the flags of
 * this area are about to be changed to vm_flags - and the no-change
 * case has already been eliminated.
 *
 * The following mprotect cases have to be considered, where AAAA is
 * the area passed down from mprotect_fixup, never extending beyond one
 * vma, PPPPPP is the prev vma specified, and NNNNNN the next vma after:
 *
 *     AAAA             AAAA                   AAAA
 *    PPPPPPNNNNNN    PPPPPPNNNNNN       PPPPPPNNNNNN
 *    cannot merge    might become       might become
 *                    PPNNNNNNNNNN       PPPPPPPPPPNN
 *    mmap, brk or    case 4 below       case 5 below
 *    mremap move:
 *                        AAAA               AAAA
 *                    PPPP    NNNN       PPPPNNNNXXXX
 *                    might become       might become
 *                    PPPPPPPPPPPP 1 or  PPPPPPPPPPPP 6 or
 *                    PPPPPPPPNNNN 2 or  PPPPPPPPXXXX 7 or
 *                    PPPPNNNNNNNN 3     PPPPXXXXXXXX 8
 *
 * It is important for case 8 that the vma NNNN overlapping the
 * region AAAA is never going to extended over XXXX. Instead XXXX must
 * be extended in region AAAA and NNNN must be removed. This way in
 * all cases where vma_merge succeeds, the moment vma_adjust drops the
 * rmap_locks, the properties of the merged vma will be already
 * correct for the whole merged range. Some of those properties like
 * vm_page_prot/vm_flags may be accessed by rmap_walks and they must
 * be correct for the whole merged range immediately after the
 * rmap_locks are released. Otherwise if XXXX would be removed and
 * NNNN would be extended over the XXXX range, remove_migration_ptes
 * or other rmap walkers (if working on addresses beyond the "end"
 * parameter) may establish ptes with the wrong permissions of NNNN
 * instead of the right permissions of XXXX.
 */
struct vm_area_struct *vma_merge(struct mm_struct *mm,
                        struct vm_area_struct *prev, unsigned long addr,
                        unsigned long end, unsigned long vm_flags,
                        struct anon_vma *anon_vma, struct file *file,
                        pgoff_t pgoff, struct mempolicy *policy,
                        struct vm_userfaultfd_ctx vm_userfaultfd_ctx)
{
        pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
        struct vm_area_struct *area, *next;
        int err;

        /*
         * We later require that vma->vm_flags == vm_flags,
         * so this tests vma->vm_flags & VM_SPECIAL, too.
         */
        if (vm_flags & VM_SPECIAL)
                return NULL;

        next = vma_next(mm, prev);
        area = next;
        if (area && area->vm_end == end)                /* cases 6, 7, 8 */
                next = next->vm_next;

        /* verify some invariant that must be enforced by the caller */
        VM_WARN_ON(prev && addr <= prev->vm_start);
        VM_WARN_ON(area && end > area->vm_end);
        VM_WARN_ON(addr >= end);

        /*
         * Can it merge with the predecessor?
         */
        if (prev && prev->vm_end == addr &&
                        mpol_equal(vma_policy(prev), policy) &&
                        can_vma_merge_after(prev, vm_flags,
                                            anon_vma, file, pgoff,
                                            vm_userfaultfd_ctx)) {
                /*
                 * OK, it can.  Can we now merge in the successor as well?
                 */
                if (next && end == next->vm_start &&
                                mpol_equal(policy, vma_policy(next)) &&
                                can_vma_merge_before(next, vm_flags,
                                                     anon_vma, file,
                                                     pgoff+pglen,
                                                     vm_userfaultfd_ctx) &&
                                is_mergeable_anon_vma(prev->anon_vma,
                                                      next->anon_vma, NULL)) {
                                                        /* cases 1, 6 */
                        err = __vma_adjust(prev, prev->vm_start,
                                         next->vm_end, prev->vm_pgoff, NULL,
                                         prev);
                } else                                  /* cases 2, 5, 7 */
                        err = __vma_adjust(prev, prev->vm_start,
                                         end, prev->vm_pgoff, NULL, prev);
                if (err)
                        return NULL;
                khugepaged_enter_vma_merge(prev, vm_flags);
                return prev;
        }

        /*
         * Can this new request be merged in front of next?
         */
        if (next && end == next->vm_start &&
                        mpol_equal(policy, vma_policy(next)) &&
                        can_vma_merge_before(next, vm_flags,
                                             anon_vma, file, pgoff+pglen,
                                             vm_userfaultfd_ctx)) {
                if (prev && addr < prev->vm_end)        /* case 4 */
                        err = __vma_adjust(prev, prev->vm_start,
                                         addr, prev->vm_pgoff, NULL, next);
                else {                                  /* cases 3, 8 */
                        err = __vma_adjust(area, addr, next->vm_end,
                                         next->vm_pgoff - pglen, NULL, next);
                        /*
                         * In case 3 area is already equal to next and
                         * this is a noop, but in case 8 "area" has
                         * been removed and next was expanded over it.
                         */
                        area = next;
                }
                if (err)
                        return NULL;
                khugepaged_enter_vma_merge(area, vm_flags);
                return area;
        }

        return NULL;
}

/*
 * Rough compatibility check to quickly see if it's even worth looking
 * at sharing an anon_vma.
 *
 * They need to have the same vm_file, and the flags can only differ
 * in things that mprotect may change.
 *
 * NOTE! The fact that we share an anon_vma doesn't _have_ to mean that
 * we can merge the two vma's. For example, we refuse to merge a vma if
 * there is a vm_ops->close() function, because that indicates that the
 * driver is doing some kind of reference counting. But that doesn't
 * really matter for the anon_vma sharing case.
 */
static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
{
        return a->vm_end == b->vm_start &&
                mpol_equal(vma_policy(a), vma_policy(b)) &&
                a->vm_file == b->vm_file &&
                !((a->vm_flags ^ b->vm_flags) & ~(VM_ACCESS_FLAGS | VM_SOFTDIRTY)) &&
                b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
}

/*
 * Do some basic sanity checking to see if we can re-use the anon_vma
 * from 'old'. The 'a'/'b' vma's are in VM order - one of them will be
 * the same as 'old', the other will be the new one that is trying
 * to share the anon_vma.
 *
 * NOTE! This runs with mm_sem held for reading, so it is possible that
 * the anon_vma of 'old' is concurrently in the process of being set up
 * by another page fault trying to merge _that_. But that's ok: if it
 * is being set up, that automatically means that it will be a singleton
 * acceptable for merging, so we can do all of this optimistically. But
 * we do that READ_ONCE() to make sure that we never re-load the pointer.
 *
 * IOW: that the "list_is_singular()" test on the anon_vma_chain only
 * matters for the 'stable anon_vma' case (ie the thing we want to avoid
 * is to return an anon_vma that is "complex" due to having gone through
 * a fork).
 *
 * We also make sure that the two vma's are compatible (adjacent,
 * and with the same memory policies). That's all stable, even with just
 * a read lock on the mm_sem.
 */
static struct anon_vma *reusable_anon_vma(struct vm_area_struct *old, struct vm_area_struct *a, struct vm_area_struct *b)
{
        if (anon_vma_compatible(a, b)) {
                struct anon_vma *anon_vma = READ_ONCE(old->anon_vma);

                if (anon_vma && list_is_singular(&old->anon_vma_chain))
                        return anon_vma;
        }
        return NULL;
}

/*
 * find_mergeable_anon_vma is used by anon_vma_prepare, to check
 * neighbouring vmas for a suitable anon_vma, before it goes off
 * to allocate a new anon_vma.  It checks because a repetitive
 * sequence of mprotects and faults may otherwise lead to distinct
 * anon_vmas being allocated, preventing vma merge in subsequent
 * mprotect.
 */
struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
{
        struct anon_vma *anon_vma = NULL;

        /* Try next first. */
        if (vma->vm_next) {
                anon_vma = reusable_anon_vma(vma->vm_next, vma, vma->vm_next);
                if (anon_vma)
                        return anon_vma;
        }

        /* Try prev next. */
        if (vma->vm_prev)
                anon_vma = reusable_anon_vma(vma->vm_prev, vma->vm_prev, vma);

        /*
         * We might reach here with anon_vma == NULL if we can't find
         * any reusable anon_vma.
         * There's no absolute need to look only at touching neighbours:
         * we could search further afield for "compatible" anon_vmas.
         * But it would probably just be a waste of time searching,
         * or lead to too many vmas hanging off the same anon_vma.
         * We're trying to allow mprotect remerging later on,
         * not trying to minimize memory used for anon_vmas.
         */
        return anon_vma;
}

/*
 * If a hint addr is less than mmap_min_addr change hint to be as
 * low as possible but still greater than mmap_min_addr
 */
static inline unsigned long round_hint_to_min(unsigned long hint)
{
        hint &= PAGE_MASK;
        if (((void *)hint != NULL) &&
            (hint < mmap_min_addr))
                return PAGE_ALIGN(mmap_min_addr);
        return hint;
}

int mlock_future_check(struct mm_struct *mm, unsigned long flags,
                       unsigned long len)
{
        unsigned long locked, lock_limit;

        /*  mlock MCL_FUTURE? */
        if (flags & VM_LOCKED) {
                locked = len >> PAGE_SHIFT;
                locked += mm->locked_vm;
                lock_limit = rlimit(RLIMIT_MEMLOCK);
                lock_limit >>= PAGE_SHIFT;
                if (locked > lock_limit && !capable(CAP_IPC_LOCK))
                        return -EAGAIN;
        }
        return 0;
}

static inline u64 file_mmap_size_max(struct file *file, struct inode *inode)
{
        if (S_ISREG(inode->i_mode))
                return MAX_LFS_FILESIZE;

        if (S_ISBLK(inode->i_mode))
                return MAX_LFS_FILESIZE;

        if (S_ISSOCK(inode->i_mode))
                return MAX_LFS_FILESIZE;

        /* Special "we do even unsigned file positions" case */
        if (file->f_mode & FMODE_UNSIGNED_OFFSET)
                return 0;

        /* Yes, random drivers might want more. But I'm tired of buggy drivers */
        return ULONG_MAX;
}

static inline bool file_mmap_ok(struct file *file, struct inode *inode,
                                unsigned long pgoff, unsigned long len)
{
        u64 maxsize = file_mmap_size_max(file, inode);

        if (maxsize && len > maxsize)
                return false;
        maxsize -= len;
        if (pgoff > maxsize >> PAGE_SHIFT)
                return false;
        return true;
}

/*
 * The caller must write-lock current->mm->mmap_lock.
 */
unsigned long do_mmap(struct file *file, unsigned long addr,
                        unsigned long len, unsigned long prot,
                        unsigned long flags, unsigned long pgoff,
                        unsigned long *populate, struct list_head *uf)
{
        struct mm_struct *mm = current->mm;
        vm_flags_t vm_flags;
        int pkey = 0;

        *populate = 0;

        if (!len)
                return -EINVAL;

        /*
         * Does the application expect PROT_READ to imply PROT_EXEC?
         *
         * (the exception is when the underlying filesystem is noexec
         *  mounted, in which case we dont add PROT_EXEC.)
         */
        if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
                if (!(file && path_noexec(&file->f_path)))
                        prot |= PROT_EXEC;

        /* force arch specific MAP_FIXED handling in get_unmapped_area */
        if (flags & MAP_FIXED_NOREPLACE)
                flags |= MAP_FIXED;

        if (!(flags & MAP_FIXED))
                addr = round_hint_to_min(addr);

        /* Careful about overflows.. */
        len = PAGE_ALIGN(len);
        if (!len)
                return -ENOMEM;

        /* offset overflow? */
        if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
                return -EOVERFLOW;

        /* Too many mappings? */
        if (mm->map_count > sysctl_max_map_count)
                return -ENOMEM;

        /* Obtain the address to map to. we verify (or select) it and ensure
         * that it represents a valid section of the address space.
         */
        addr = get_unmapped_area(file, addr, len, pgoff, flags);
        if (IS_ERR_VALUE(addr))
                return addr;

        if (flags & MAP_FIXED_NOREPLACE) {
                if (find_vma_intersection(mm, addr, addr + len))
                        return -EEXIST;
        }

        if (prot == PROT_EXEC) {
                pkey = execute_only_pkey(mm);
                if (pkey < 0)
                        pkey = 0;
        }

        /* Do simple checking here so the lower-level routines won't have
         * to. we assume access permissions have been handled by the open
         * of the memory object, so we don't do any here.
         */
        vm_flags = calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
                        mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

        if (flags & MAP_LOCKED)
                if (!can_do_mlock())
                        return -EPERM;

        if (mlock_future_check(mm, vm_flags, len))
                return -EAGAIN;

        if (file) {
                struct inode *inode = file_inode(file);
                unsigned long flags_mask;

                if (!file_mmap_ok(file, inode, pgoff, len))
                        return -EOVERFLOW;

                flags_mask = LEGACY_MAP_MASK | file->f_op->mmap_supported_flags;

                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        /*
                         * Force use of MAP_SHARED_VALIDATE with non-legacy
                         * flags. E.g. MAP_SYNC is dangerous to use with
                         * MAP_SHARED as you don't know which consistency model
                         * you will get. We silently ignore unsupported flags
                         * with MAP_SHARED to preserve backward compatibility.
                         */
                        flags &= LEGACY_MAP_MASK;
                        fallthrough;
                case MAP_SHARED_VALIDATE:
                        if (flags & ~flags_mask)
                                return -EOPNOTSUPP;
                        if (prot & PROT_WRITE) {
                                if (!(file->f_mode & FMODE_WRITE))
                                        return -EACCES;
                                if (IS_SWAPFILE(file->f_mapping->host))
                                        return -ETXTBSY;
                        }

                        /*
                         * Make sure we don't allow writing to an append-only
                         * file..
                         */
                        if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
                                return -EACCES;

                        vm_flags |= VM_SHARED | VM_MAYSHARE;
                        if (!(file->f_mode & FMODE_WRITE))
                                vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
                        fallthrough;
                case MAP_PRIVATE:
                        if (!(file->f_mode & FMODE_READ))
                                return -EACCES;
                        if (path_noexec(&file->f_path)) {
                                if (vm_flags & VM_EXEC)
                                        return -EPERM;
                                vm_flags &= ~VM_MAYEXEC;
                        }

                        if (!file->f_op->mmap)
                                return -ENODEV;
                        if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                                return -EINVAL;
                        break;

                default:
                        return -EINVAL;
                }
        } else {
                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                                return -EINVAL;
                        /*
                         * Ignore pgoff.
                         */
                        pgoff = 0;
                        vm_flags |= VM_SHARED | VM_MAYSHARE;
                        break;
                case MAP_PRIVATE:
                        /*
                         * Set pgoff according to addr for anon_vma.
                         */
                        pgoff = addr >> PAGE_SHIFT;
                        break;
                default:
                        return -EINVAL;
                }
        }

        /*
         * Set 'VM_NORESERVE' if we should not account for the
         * memory use of this mapping.
         */
        if (flags & MAP_NORESERVE) {
                /* We honor MAP_NORESERVE if allowed to overcommit */
                if (sysctl_overcommit_memory != OVERCOMMIT_NEVER)
                        vm_flags |= VM_NORESERVE;

                /* hugetlb applies strict overcommit unless MAP_NORESERVE */
                if (file && is_file_hugepages(file))
                        vm_flags |= VM_NORESERVE;
        }

        addr = mmap_region(file, addr, len, vm_flags, pgoff, uf);
        if (!IS_ERR_VALUE(addr) &&
            ((vm_flags & VM_LOCKED) ||
             (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
                *populate = len;
        return addr;
}

unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
                              unsigned long prot, unsigned long flags,
                              unsigned long fd, unsigned long pgoff)
{
        struct file *file = NULL;
        unsigned long retval;

        if (!(flags & MAP_ANONYMOUS)) {
                audit_mmap_fd(fd, flags);
                file = fget(fd);
                if (!file)
                        return -EBADF;
                if (is_file_hugepages(file)) {
                        len = ALIGN(len, huge_page_size(hstate_file(file)));
                } else if (unlikely(flags & MAP_HUGETLB)) {
                        retval = -EINVAL;
                        goto out_fput;
                }
        } else if (flags & MAP_HUGETLB) {
                struct ucounts *ucounts = NULL;
                struct hstate *hs;

                hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
                if (!hs)
                        return -EINVAL;

                len = ALIGN(len, huge_page_size(hs));
                /*
                 * VM_NORESERVE is used because the reservations will be
                 * taken when vm_ops->mmap() is called
                 * A dummy user value is used because we are not locking
                 * memory so no accounting is necessary
                 */
                file = hugetlb_file_setup(HUGETLB_ANON_FILE, len,
                                VM_NORESERVE,
                                &ucounts, HUGETLB_ANONHUGE_INODE,
                                (flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
                if (IS_ERR(file))
                        return PTR_ERR(file);
        }

        flags &= ~MAP_DENYWRITE;

        retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
out_fput:
        if (file)
                fput(file);
        return retval;
}

SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
                unsigned long, prot, unsigned long, flags,
                unsigned long, fd, unsigned long, pgoff)
{
        return ksys_mmap_pgoff(addr, len, prot, flags, fd, pgoff);
}

#ifdef __ARCH_WANT_SYS_OLD_MMAP
struct mmap_arg_struct {
        unsigned long addr;
        unsigned long len;
        unsigned long prot;
        unsigned long flags;
        unsigned long fd;
        unsigned long offset;
};

SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
{
        struct mmap_arg_struct a;

        if (copy_from_user(&a, arg, sizeof(a)))
                return -EFAULT;
        if (offset_in_page(a.offset))
                return -EINVAL;

        return ksys_mmap_pgoff(a.addr, a.len, a.prot, a.flags, a.fd,
                               a.offset >> PAGE_SHIFT);
}
#endif /* __ARCH_WANT_SYS_OLD_MMAP */

/*
 * Some shared mappings will want the pages marked read-only
 * to track write events. If so, we'll downgrade vm_page_prot
 * to the private version (using protection_map[] without the
 * VM_SHARED bit).
 */
int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
{
        vm_flags_t vm_flags = vma->vm_flags;
        const struct vm_operations_struct *vm_ops = vma->vm_ops;

        /* If it was private or non-writable, the write bit is already clear */
        if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED)))
                return 0;

        /* The backer wishes to know when pages are first written to? */
        if (vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite))
                return 1;

        /* The open routine did something to the protections that pgprot_modify
         * won't preserve? */
        if (pgprot_val(vm_page_prot) !=
            pgprot_val(vm_pgprot_modify(vm_page_prot, vm_flags)))
                return 0;

        /* Do we need to track softdirty? */
        if (IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) && !(vm_flags & VM_SOFTDIRTY))
                return 1;

        /* Specialty mapping? */
        if (vm_flags & VM_PFNMAP)
                return 0;

        /* Can the mapping track the dirty pages? */
        return vma->vm_file && vma->vm_file->f_mapping &&
                mapping_can_writeback(vma->vm_file->f_mapping);
}

/*
 * We account for memory if it's a private writeable mapping,
 * not hugepages and VM_NORESERVE wasn't set.
 */
static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
{
        /*
         * hugetlb has its own accounting separate from the core VM
         * VM_HUGETLB may not be set yet so we cannot check for that flag.
         */
        if (file && is_file_hugepages(file))
                return 0;

        return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
}

unsigned long mmap_region(struct file *file, unsigned long addr,
                unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
                struct list_head *uf)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma, *prev, *merge;
        int error;
        struct rb_node **rb_link, *rb_parent;
        unsigned long charged = 0;

        /* Check against address space limit. */
        if (!may_expand_vm(mm, vm_flags, len >> PAGE_SHIFT)) {
                unsigned long nr_pages;

                /*
                 * MAP_FIXED may remove pages of mappings that intersects with
                 * requested mapping. Account for the pages it would unmap.
                 */
                nr_pages = count_vma_pages_range(mm, addr, addr + len);

                if (!may_expand_vm(mm, vm_flags,
                                        (len >> PAGE_SHIFT) - nr_pages))
                        return -ENOMEM;
        }

        /* Clear old maps, set up prev, rb_link, rb_parent, and uf */
        if (munmap_vma_range(mm, addr, len, &prev, &rb_link, &rb_parent, uf))
                return -ENOMEM;
        /*
         * Private writable mapping: check memory availability
         */
        if (accountable_mapping(file, vm_flags)) {
                charged = len >> PAGE_SHIFT;
                if (security_vm_enough_memory_mm(mm, charged))
                        return -ENOMEM;
                vm_flags |= VM_ACCOUNT;
        }

        /*
         * Can we just expand an old mapping?
         */
        vma = vma_merge(mm, prev, addr, addr + len, vm_flags,
                        NULL, file, pgoff, NULL, NULL_VM_UFFD_CTX);
        if (vma)
                goto out;

        /*
         * Determine the object being mapped and call the appropriate
         * specific mapper. the address has already been validated, but
         * not unmapped, but the maps are removed from the list.
         */
        vma = vm_area_alloc(mm);
        if (!vma) {
                error = -ENOMEM;
                goto unacct_error;
        }

        vma->vm_start = addr;
        vma->vm_end = addr + len;
        vma->vm_flags = vm_flags;
        vma->vm_page_prot = vm_get_page_prot(vm_flags);
        vma->vm_pgoff = pgoff;

        if (file) {
                if (vm_flags & VM_DENYWRITE) {
                        error = deny_write_access(file);
                        if (error)
                                goto free_vma;
                }
                if (vm_flags & VM_SHARED) {
                        error = mapping_map_writable(file->f_mapping);
                        if (error)
                                goto allow_write_and_free_vma;
                }

                /* ->mmap() can change vma->vm_file, but must guarantee that
                 * vma_link() below can deny write-access if VM_DENYWRITE is set
                 * and map writably if VM_SHARED is set. This usually means the
                 * new file must not have been exposed to user-space, yet.
                 */
                vma->vm_file = get_file(file);
                error = call_mmap(file, vma);
                if (error)
                        goto unmap_and_free_vma;

                /* Can addr have changed??
                 *
                 * Answer: Yes, several device drivers can do it in their
                 *         f_op->mmap method. -DaveM
                 * Bug: If addr is changed, prev, rb_link, rb_parent should
                 *      be updated for vma_link()
                 */
                WARN_ON_ONCE(addr != vma->vm_start);

                addr = vma->vm_start;

                /* If vm_flags changed after call_mmap(), we should try merge vma again
                 * as we may succeed this time.
                 */
                if (unlikely(vm_flags != vma->vm_flags && prev)) {
                        merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags,
                                NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX);
                        if (merge) {
                                /* ->mmap() can change vma->vm_file and fput the original file. So
                                 * fput the vma->vm_file here or we would add an extra fput for file
                                 * and cause general protection fault ultimately.
                                 */
                                fput(vma->vm_file);
                                vm_area_free(vma);
                                vma = merge;
                                /* Update vm_flags to pick up the change. */
                                vm_flags = vma->vm_flags;
                                goto unmap_writable;
                        }
                }

                vm_flags = vma->vm_flags;
        } else if (vm_flags & VM_SHARED) {
                error = shmem_zero_setup(vma);
                if (error)
                        goto free_vma;
        } else {
                vma_set_anonymous(vma);
        }

        /* Allow architectures to sanity-check the vm_flags */
        if (!arch_validate_flags(vma->vm_flags)) {
                error = -EINVAL;
                if (file)
                        goto unmap_and_free_vma;
                else
                        goto free_vma;
        }

        vma_link(mm, vma, prev, rb_link, rb_parent);
        /* Once vma denies write, undo our temporary denial count */
        if (file) {
unmap_writable:
                if (vm_flags & VM_SHARED)
                        mapping_unmap_writable(file->f_mapping);
                if (vm_flags & VM_DENYWRITE)
                        allow_write_access(file);
        }
        file = vma->vm_file;
out:
        perf_event_mmap(vma);

        vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
        if (vm_flags & VM_LOCKED) {
                if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
                                        is_vm_hugetlb_page(vma) ||
                                        vma == get_gate_vma(current->mm))
                        vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
                else
                        mm->locked_vm += (len >> PAGE_SHIFT);
        }

        if (file)
                uprobe_mmap(vma);

        /*
         * New (or expanded) vma always get soft dirty status.
         * Otherwise user-space soft-dirty page tracker won't
         * be able to distinguish situation when vma area unmapped,
         * then new mapped in-place (which must be aimed as
         * a completely new data area).
         */
        vma->vm_flags |= VM_SOFTDIRTY;

        vma_set_page_prot(vma);

        return addr;

unmap_and_free_vma:
        fput(vma->vm_file);
        vma->vm_file = NULL;

        /* Undo any partial mapping done by a device driver. */
        unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
        charged = 0;
        if (vm_flags & VM_SHARED)
                mapping_unmap_writable(file->f_mapping);
allow_write_and_free_vma:
        if (vm_flags & VM_DENYWRITE)
                allow_write_access(file);
free_vma:
        vm_area_free(vma);
unacct_error:
        if (charged)
                vm_unacct_memory(charged);
        return error;
}

static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
{
        /*
         * We implement the search by looking for an rbtree node that
         * immediately follows a suitable gap. That is,
         * - gap_start = vma->vm_prev->vm_end <= info->high_limit - length;
         * - gap_end   = vma->vm_start        >= info->low_limit  + length;
         * - gap_end - gap_start >= length
         */

        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long length, low_limit, high_limit, gap_start, gap_end;

        /* Adjust search length to account for worst case alignment overhead */
        length = info->length + info->align_mask;
        if (length < info->length)
                return -ENOMEM;

        /* Adjust search limits by the desired length */
        if (info->high_limit < length)
                return -ENOMEM;
        high_limit = info->high_limit - length;

        if (info->low_limit > high_limit)
                return -ENOMEM;
        low_limit = info->low_limit + length;

        /* Check if rbtree root looks promising */
        if (RB_EMPTY_ROOT(&mm->mm_rb))
                goto check_highest;
        vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
        if (vma->rb_subtree_gap < length)
                goto check_highest;

        while (true) {
                /* Visit left subtree if it looks promising */
                gap_end = vm_start_gap(vma);
                if (gap_end >= low_limit && vma->vm_rb.rb_left) {
                        struct vm_area_struct *left =
                                rb_entry(vma->vm_rb.rb_left,
                                         struct vm_area_struct, vm_rb);
                        if (left->rb_subtree_gap >= length) {
                                vma = left;
                                continue;
                        }
                }

                gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
check_current:
                /* Check if current node has a suitable gap */
                if (gap_start > high_limit)
                        return -ENOMEM;
                if (gap_end >= low_limit &&
                    gap_end > gap_start && gap_end - gap_start >= length)
                        goto found;

                /* Visit right subtree if it looks promising */
                if (vma->vm_rb.rb_right) {
                        struct vm_area_struct *right =
                                rb_entry(vma->vm_rb.rb_right,
                                         struct vm_area_struct, vm_rb);
                        if (right->rb_subtree_gap >= length) {
                                vma = right;
                                continue;
                        }
                }

                /* Go back up the rbtree to find next candidate node */
                while (true) {
                        struct rb_node *prev = &vma->vm_rb;
                        if (!rb_parent(prev))
                                goto check_highest;
                        vma = rb_entry(rb_parent(prev),
                                       struct vm_area_struct, vm_rb);
                        if (prev == vma->vm_rb.rb_left) {
                                gap_start = vm_end_gap(vma->vm_prev);
                                gap_end = vm_start_gap(vma);
                                goto check_current;
                        }
                }
        }

check_highest:
        /* Check highest gap, which does not precede any rbtree node */
        gap_start = mm->highest_vm_end;
        gap_end = ULONG_MAX;  /* Only for VM_BUG_ON below */
        if (gap_start > high_limit)
                return -ENOMEM;

found:
        /* We found a suitable gap. Clip it with the original low_limit. */
        if (gap_start < info->low_limit)
                gap_start = info->low_limit;

        /* Adjust gap address to the desired alignment */
        gap_start += (info->align_offset - gap_start) & info->align_mask;

        VM_BUG_ON(gap_start + info->length > info->high_limit);
        VM_BUG_ON(gap_start + info->length > gap_end);
        return gap_start;
}

static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long length, low_limit, high_limit, gap_start, gap_end;

        /* Adjust search length to account for worst case alignment overhead */
        length = info->length + info->align_mask;
        if (length < info->length)
                return -ENOMEM;

        /*
         * Adjust search limits by the desired length.
         * See implementation comment at top of unmapped_area().
         */
        gap_end = info->high_limit;
        if (gap_end < length)
                return -ENOMEM;
        high_limit = gap_end - length;

        if (info->low_limit > high_limit)
                return -ENOMEM;
        low_limit = info->low_limit + length;

        /* Check highest gap, which does not precede any rbtree node */
        gap_start = mm->highest_vm_end;
        if (gap_start <= high_limit)
                goto found_highest;

        /* Check if rbtree root looks promising */
        if (RB_EMPTY_ROOT(&mm->mm_rb))
                return -ENOMEM;
        vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
        if (vma->rb_subtree_gap < length)
                return -ENOMEM;

        while (true) {
                /* Visit right subtree if it looks promising */
                gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
                if (gap_start <= high_limit && vma->vm_rb.rb_right) {
                        struct vm_area_struct *right =
                                rb_entry(vma->vm_rb.rb_right,
                                         struct vm_area_struct, vm_rb);
                        if (right->rb_subtree_gap >= length) {
                                vma = right;
                                continue;
                        }
                }

check_current:
                /* Check if current node has a suitable gap */
                gap_end = vm_start_gap(vma);
                if (gap_end < low_limit)
                        return -ENOMEM;
                if (gap_start <= high_limit &&
                    gap_end > gap_start && gap_end - gap_start >= length)
                        goto found;

                /* Visit left subtree if it looks promising */
                if (vma->vm_rb.rb_left) {
                        struct vm_area_struct *left =
                                rb_entry(vma->vm_rb.rb_left,
                                         struct vm_area_struct, vm_rb);
                        if (left->rb_subtree_gap >= length) {
                                vma = left;
                                continue;
                        }
                }

                /* Go back up the rbtree to find next candidate node */
                while (true) {
                        struct rb_node *prev = &vma->vm_rb;
                        if (!rb_parent(prev))
                                return -ENOMEM;
                        vma = rb_entry(rb_parent(prev),
                                       struct vm_area_struct, vm_rb);
                        if (prev == vma->vm_rb.rb_right) {
                                gap_start = vma->vm_prev ?
                                        vm_end_gap(vma->vm_prev) : 0;
                                goto check_current;
                        }
                }
        }

found:
        /* We found a suitable gap. Clip it with the original high_limit. */
        if (gap_end > info->high_limit)
                gap_end = info->high_limit;

found_highest:
        /* Compute highest gap address at the desired alignment */
        gap_end -= info->length;
        gap_end -= (gap_end - info->align_offset) & info->align_mask;

        VM_BUG_ON(gap_end < info->low_limit);
        VM_BUG_ON(gap_end < gap_start);
        return gap_end;
}

/*
 * Search for an unmapped address range.
 *
 * We are looking for a range that:
 * - does not intersect with any VMA;
 * - is contained within the [low_limit, high_limit) interval;
 * - is at least the desired size.
 * - satisfies (begin_addr & align_mask) == (align_offset & align_mask)
 */
unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info)
{
        unsigned long addr;

        if (info->flags & VM_UNMAPPED_AREA_TOPDOWN)
                addr = unmapped_area_topdown(info);
        else
                addr = unmapped_area(info);

        trace_vm_unmapped_area(addr, info);
        return addr;
}

#ifndef arch_get_mmap_end
#define arch_get_mmap_end(addr) (TASK_SIZE)
#endif

#ifndef arch_get_mmap_base
#define arch_get_mmap_base(addr, base) (base)
#endif

/* Get an address range which is currently unmapped.
 * For shmat() with addr=0.
 *
 * Ugly calling convention alert:
 * Return value with the low bits set means error value,
 * ie
 *      if (ret & ~PAGE_MASK)
 *              error = ret;
 *
 * This function "knows" that -ENOMEM has the bits set.
 */
#ifndef HAVE_ARCH_UNMAPPED_AREA
unsigned long
arch_get_unmapped_area(struct file *filp, unsigned long addr,
                unsigned long len, unsigned long pgoff, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma, *prev;
        struct vm_unmapped_area_info info;
        const unsigned long mmap_end = arch_get_mmap_end(addr);

        if (len > mmap_end - mmap_min_addr)
                return -ENOMEM;

        if (flags & MAP_FIXED)
                return addr;

        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma_prev(mm, addr, &prev);
                if (mmap_end - len >= addr && addr >= mmap_min_addr &&
                    (!vma || addr + len <= vm_start_gap(vma)) &&
                    (!prev || addr >= vm_end_gap(prev)))
                        return addr;
        }

        info.flags = 0;
        info.length = len;
        info.low_limit = mm->mmap_base;
        info.high_limit = mmap_end;
        info.align_mask = 0;
        info.align_offset = 0;
        return vm_unmapped_area(&info);
}
#endif

/*
 * This mmap-allocator allocates new areas top-down from below the
 * stack's low limit (the base):
 */
#ifndef HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
unsigned long
arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
                          unsigned long len, unsigned long pgoff,
                          unsigned long flags)
{
        struct vm_area_struct *vma, *prev;
        struct mm_struct *mm = current->mm;
        struct vm_unmapped_area_info info;
        const unsigned long mmap_end = arch_get_mmap_end(addr);

        /* requested length too big for entire address space */
        if (len > mmap_end - mmap_min_addr)
                return -ENOMEM;

        if (flags & MAP_FIXED)
                return addr;

        /* requesting a specific address */
        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma_prev(mm, addr, &prev);
                if (mmap_end - len >= addr && addr >= mmap_min_addr &&
                                (!vma || addr + len <= vm_start_gap(vma)) &&
                                (!prev || addr >= vm_end_gap(prev)))
                        return addr;
        }

        info.flags = VM_UNMAPPED_AREA_TOPDOWN;
        info.length = len;
        info.low_limit = max(PAGE_SIZE, mmap_min_addr);
        info.high_limit = arch_get_mmap_base(addr, mm->mmap_base);
        info.align_mask = 0;
        info.align_offset = 0;
        addr = vm_unmapped_area(&info);

        /*
         * A failed mmap() very likely causes application failure,
         * so fall back to the bottom-up function here. This scenario
         * can happen with large stack limits and large mmap()
         * allocations.
         */
        if (offset_in_page(addr)) {
                VM_BUG_ON(addr != -ENOMEM);
                info.flags = 0;
                info.low_limit = TASK_UNMAPPED_BASE;
                info.high_limit = mmap_end;
                addr = vm_unmapped_area(&info);
        }

        return addr;
}
#endif

unsigned long
get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
                unsigned long pgoff, unsigned long flags)
{
        unsigned long (*get_area)(struct file *, unsigned long,
                                  unsigned long, unsigned long, unsigned long);

        unsigned long error = arch_mmap_check(addr, len, flags);
        if (error)
                return error;

        /* Careful about overflows.. */
        if (len > TASK_SIZE)
                return -ENOMEM;

        get_area = current->mm->get_unmapped_area;
        if (file) {
                if (file->f_op->get_unmapped_area)
                        get_area = file->f_op->get_unmapped_area;
        } else if (flags & MAP_SHARED) {
                /*
                 * mmap_region() will call shmem_zero_setup() to create a file,
                 * so use shmem's get_unmapped_area in case it can be huge.
                 * do_mmap() will clear pgoff, so match alignment.
                 */
                pgoff = 0;
                get_area = shmem_get_unmapped_area;
        }

        addr = get_area(file, addr, len, pgoff, flags);
        if (IS_ERR_VALUE(addr))
                return addr;

        if (addr > TASK_SIZE - len)
                return -ENOMEM;
        if (offset_in_page(addr))
                return -EINVAL;

        error = security_mmap_addr(addr);
        return error ? error : addr;
}

EXPORT_SYMBOL(get_unmapped_area);

/* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
{
        struct rb_node *rb_node;
        struct vm_area_struct *vma;

        mmap_assert_locked(mm);
        /* Check the cache first. */
        vma = vmacache_find(mm, addr);
        if (likely(vma))
                return vma;

        rb_node = mm->mm_rb.rb_node;

        while (rb_node) {
                struct vm_area_struct *tmp;

                tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);

                if (tmp->vm_end > addr) {
                        vma = tmp;
                        if (tmp->vm_start <= addr)
                                break;
                        rb_node = rb_node->rb_left;
                } else
                        rb_node = rb_node->rb_right;
        }

        if (vma)
                vmacache_update(addr, vma);
        return vma;
}

EXPORT_SYMBOL(find_vma);

/*
 * Same as find_vma, but also return a pointer to the previous VMA in *pprev.
 */
struct vm_area_struct *
find_vma_prev(struct mm_struct *mm, unsigned long addr,
                        struct vm_area_struct **pprev)
{
        struct vm_area_struct *vma;

        vma = find_vma(mm, addr);
        if (vma) {
                *pprev = vma->vm_prev;
        } else {
                struct rb_node *rb_node = rb_last(&mm->mm_rb);

                *pprev = rb_node ? rb_entry(rb_node, struct vm_area_struct, vm_rb) : NULL;
        }
        return vma;
}

/*
 * Verify that the stack growth is acceptable and
 * update accounting. This is shared with both the
 * grow-up and grow-down cases.
 */
static int acct_stack_growth(struct vm_area_struct *vma,
                             unsigned long size, unsigned long grow)
{
        struct mm_struct *mm = vma->vm_mm;
        unsigned long new_start;

        /* address space limit tests */
        if (!may_expand_vm(mm, vma->vm_flags, grow))
                return -ENOMEM;

        /* Stack limit test */
        if (size > rlimit(RLIMIT_STACK))
                return -ENOMEM;

        /* mlock limit tests */
        if (vma->vm_flags & VM_LOCKED) {
                unsigned long locked;
                unsigned long limit;
                locked = mm->locked_vm + grow;
                limit = rlimit(RLIMIT_MEMLOCK);
                limit >>= PAGE_SHIFT;
                if (locked > limit && !capable(CAP_IPC_LOCK))
                        return -ENOMEM;
        }

        /* Check to ensure the stack will not grow into a hugetlb-only region */
        new_start = (vma->vm_flags & VM_GROWSUP) ? vma->vm_start :
                        vma->vm_end - size;
        if (is_hugepage_only_range(vma->vm_mm, new_start, size))
                return -EFAULT;

        /*
         * Overcommit..  This must be the final test, as it will
         * update security statistics.
         */
        if (security_vm_enough_memory_mm(mm, grow))
                return -ENOMEM;

        return 0;
}

#if defined(CONFIG_STACK_GROWSUP) || defined(CONFIG_IA64)
/*
 * PA-RISC uses this for its stack; IA64 for its Register Backing Store.
 * vma is the last one with address > vma->vm_end.  Have to extend vma.
 */
int expand_upwards(struct vm_area_struct *vma, unsigned long address)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *next;
        unsigned long gap_addr;
        int error = 0;

        if (!(vma->vm_flags & VM_GROWSUP))
                return -EFAULT;

        /* Guard against exceeding limits of the address space. */
        address &= PAGE_MASK;
        if (address >= (TASK_SIZE & PAGE_MASK))
                return -ENOMEM;
        address += PAGE_SIZE;

        /* Enforce stack_guard_gap */
        gap_addr = address + stack_guard_gap;

        /* Guard against overflow */
        if (gap_addr < address || gap_addr > TASK_SIZE)
                gap_addr = TASK_SIZE;

        next = vma->vm_next;
        if (next && next->vm_start < gap_addr && vma_is_accessible(next)) {
                if (!(next->vm_flags & VM_GROWSUP))
                        return -ENOMEM;
                /* Check that both stack segments have the same anon_vma? */
        }

        /* We must make sure the anon_vma is allocated. */
        if (unlikely(anon_vma_prepare(vma)))
                return -ENOMEM;

        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_lock in read mode.  We need the
         * anon_vma lock to serialize against concurrent expand_stacks.
         */
        anon_vma_lock_write(vma->anon_vma);

        /* Somebody else might have raced and expanded it already */
        if (address > vma->vm_end) {
                unsigned long size, grow;

                size = address - vma->vm_start;
                grow = (address - vma->vm_end) >> PAGE_SHIFT;

                error = -ENOMEM;
                if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) {
                        error = acct_stack_growth(vma, size, grow);
                        if (!error) {
                                /*
                                 * vma_gap_update() doesn't support concurrent
                                 * updates, but we only hold a shared mmap_lock
                                 * lock here, so we need to protect against
                                 * concurrent vma expansions.
                                 * anon_vma_lock_write() doesn't help here, as
                                 * we don't guarantee that all growable vmas
                                 * in a mm share the same root anon vma.
                                 * So, we reuse mm->page_table_lock to guard
                                 * against concurrent vma expansions.
                                 */
                                spin_lock(&mm->page_table_lock);
                                if (vma->vm_flags & VM_LOCKED)
                                        mm->locked_vm += grow;
                                vm_stat_account(mm, vma->vm_flags, grow);
                                anon_vma_interval_tree_pre_update_vma(vma);
                                vma->vm_end = address;
                                anon_vma_interval_tree_post_update_vma(vma);
                                if (vma->vm_next)
                                        vma_gap_update(vma->vm_next);
                                else
                                        mm->highest_vm_end = vm_end_gap(vma);
                                spin_unlock(&mm->page_table_lock);

                                perf_event_mmap(vma);
                        }
                }
        }
        anon_vma_unlock_write(vma->anon_vma);
        khugepaged_enter_vma_merge(vma, vma->vm_flags);
        validate_mm(mm);
        return error;
}
#endif /* CONFIG_STACK_GROWSUP || CONFIG_IA64 */

/*
 * vma is the first one with address < vma->vm_start.  Have to extend vma.
 */
int expand_downwards(struct vm_area_struct *vma,
                                   unsigned long address)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *prev;
        int error = 0;

        address &= PAGE_MASK;
        if (address < mmap_min_addr)
                return -EPERM;

        /* Enforce stack_guard_gap */
        prev = vma->vm_prev;
        /* Check that both stack segments have the same anon_vma? */
        if (prev && !(prev->vm_flags & VM_GROWSDOWN) &&
                        vma_is_accessible(prev)) {
                if (address - prev->vm_end < stack_guard_gap)
                        return -ENOMEM;
        }

        /* We must make sure the anon_vma is allocated. */
        if (unlikely(anon_vma_prepare(vma)))
                return -ENOMEM;

        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_lock in read mode.  We need the
         * anon_vma lock to serialize against concurrent expand_stacks.
         */
        anon_vma_lock_write(vma->anon_vma);

        /* Somebody else might have raced and expanded it already */
        if (address < vma->vm_start) {
                unsigned long size, grow;

                size = vma->vm_end - address;
                grow = (vma->vm_start - address) >> PAGE_SHIFT;

                error = -ENOMEM;
                if (grow <= vma->vm_pgoff) {
                        error = acct_stack_growth(vma, size, grow);
                        if (!error) {
                                /*
                                 * vma_gap_update() doesn't support concurrent
                                 * updates, but we only hold a shared mmap_lock
                                 * lock here, so we need to protect against
                                 * concurrent vma expansions.
                                 * anon_vma_lock_write() doesn't help here, as
                                 * we don't guarantee that all growable vmas
                                 * in a mm share the same root anon vma.
                                 * So, we reuse mm->page_table_lock to guard
                                 * against concurrent vma expansions.
                                 */
                                spin_lock(&mm->page_table_lock);
                                if (vma->vm_flags & VM_LOCKED)
                                        mm->locked_vm += grow;
                                vm_stat_account(mm, vma->vm_flags, grow);
                                anon_vma_interval_tree_pre_update_vma(vma);
                                vma->vm_start = address;
                                vma->vm_pgoff -= grow;
                                anon_vma_interval_tree_post_update_vma(vma);
                                vma_gap_update(vma);
                                spin_unlock(&mm->page_table_lock);

                                perf_event_mmap(vma);
                        }
                }
        }
        anon_vma_unlock_write(vma->anon_vma);
        khugepaged_enter_vma_merge(vma, vma->vm_flags);
        validate_mm(mm);
        return error;
}

/* enforced gap between the expanding stack and other mappings. */
unsigned long stack_guard_gap = 256UL<<PAGE_SHIFT;

static int __init cmdline_parse_stack_guard_gap(char *p)
{
        unsigned long val;
        char *endptr;

        val = simple_strtoul(p, &endptr, 10);
        if (!*endptr)
                stack_guard_gap = val << PAGE_SHIFT;

        return 0;
}
__setup("stack_guard_gap=", cmdline_parse_stack_guard_gap);

#ifdef CONFIG_STACK_GROWSUP
int expand_stack(struct vm_area_struct *vma, unsigned long address)
{
        return expand_upwards(vma, address);
}

struct vm_area_struct *
find_extend_vma(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma, *prev;

        addr &= PAGE_MASK;
        vma = find_vma_prev(mm, addr, &prev);
        if (vma && (vma->vm_start <= addr))
                return vma;
        /* don't alter vm_end if the coredump is running */
        if (!prev || expand_stack(prev, addr))
                return NULL;
        if (prev->vm_flags & VM_LOCKED)
                populate_vma_page_range(prev, addr, prev->vm_end, NULL);
        return prev;
}
#else
int expand_stack(struct vm_area_struct *vma, unsigned long address)
{
        return expand_downwards(vma, address);
}

struct vm_area_struct *
find_extend_vma(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma;
        unsigned long start;

        addr &= PAGE_MASK;
        vma = find_vma(mm, addr);
        if (!vma)
                return NULL;
        if (vma->vm_start <= addr)
                return vma;
        if (!(vma->vm_flags & VM_GROWSDOWN))
                return NULL;
        start = vma->vm_start;
        if (expand_stack(vma, addr))
                return NULL;
        if (vma->vm_flags & VM_LOCKED)
                populate_vma_page_range(vma, addr, start, NULL);
        return vma;
}
#endif

EXPORT_SYMBOL_GPL(find_extend_vma);

/*
 * Ok - we have the memory areas we should free on the vma list,
 * so release them, and do the vma updates.
 *
 * Called with the mm semaphore held.
 */
static void remove_vma_list(struct mm_struct *mm, struct vm_area_struct *vma)
{
        unsigned long nr_accounted = 0;

        /* Update high watermark before we lower total_vm */
        update_hiwater_vm(mm);
        do {
                long nrpages = vma_pages(vma);

                if (vma->vm_flags & VM_ACCOUNT)
                        nr_accounted += nrpages;
                vm_stat_account(mm, vma->vm_flags, -nrpages);
                vma = remove_vma(vma);
        } while (vma);
        vm_unacct_memory(nr_accounted);
        validate_mm(mm);
}

/*
 * Get rid of page table information in the indicated region.
 *
 * Called with the mm semaphore held.
 */
static void unmap_region(struct mm_struct *mm,
                struct vm_area_struct *vma, struct vm_area_struct *prev,
                unsigned long start, unsigned long end)
{
        struct vm_area_struct *next = vma_next(mm, prev);
        struct mmu_gather tlb;

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm);
        update_hiwater_rss(mm);
        unmap_vmas(&tlb, vma, start, end);
        free_pgtables(&tlb, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
                                 next ? next->vm_start : USER_PGTABLES_CEILING);
        tlb_finish_mmu(&tlb);
}

/*
 * Create a list of vma's touched by the unmap, removing them from the mm's
 * vma list as we go..
 */
static bool
detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
        struct vm_area_struct *prev, unsigned long end)
{
        struct vm_area_struct **insertion_point;
        struct vm_area_struct *tail_vma = NULL;

        insertion_point = (prev ? &prev->vm_next : &mm->mmap);
        vma->vm_prev = NULL;
        do {
                vma_rb_erase(vma, &mm->mm_rb);
                mm->map_count--;
                tail_vma = vma;
                vma = vma->vm_next;
        } while (vma && vma->vm_start < end);
        *insertion_point = vma;
        if (vma) {
                vma->vm_prev = prev;
                vma_gap_update(vma);
        } else
                mm->highest_vm_end = prev ? vm_end_gap(prev) : 0;
        tail_vma->vm_next = NULL;

        /* Kill the cache */
        vmacache_invalidate(mm);

        /*
         * Do not downgrade mmap_lock if we are next to VM_GROWSDOWN or
         * VM_GROWSUP VMA. Such VMAs can change their size under
         * down_read(mmap_lock) and collide with the VMA we are about to unmap.
         */
        if (vma && (vma->vm_flags & VM_GROWSDOWN))
                return false;
        if (prev && (prev->vm_flags & VM_GROWSUP))
                return false;
        return true;
}

/*
 * __split_vma() bypasses sysctl_max_map_count checking.  We use this where it
 * has already been checked or doesn't make sense to fail.
 */
int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
                unsigned long addr, int new_below)
{
        struct vm_area_struct *new;
        int err;

        if (vma->vm_ops && vma->vm_ops->may_split) {
                err = vma->vm_ops->may_split(vma, addr);
                if (err)
                        return err;
        }

        new = vm_area_dup(vma);
        if (!new)
                return -ENOMEM;

        if (new_below)
                new->vm_end = addr;
        else {
                new->vm_start = addr;
                new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
        }

        err = vma_dup_policy(vma, new);
        if (err)
                goto out_free_vma;

        err = anon_vma_clone(new, vma);
        if (err)
                goto out_free_mpol;

        if (new->vm_file)
                get_file(new->vm_file);

        if (new->vm_ops && new->vm_ops->open)
                new->vm_ops->open(new);

        if (new_below)
                err = vma_adjust(vma, addr, vma->vm_end, vma->vm_pgoff +
                        ((addr - new->vm_start) >> PAGE_SHIFT), new);
        else
                err = vma_adjust(vma, vma->vm_start, addr, vma->vm_pgoff, new);

        /* Success. */
        if (!err)
                return 0;

        /* Clean everything up if vma_adjust failed. */
        if (new->vm_ops && new->vm_ops->close)
                new->vm_ops->close(new);
        if (new->vm_file)
                fput(new->vm_file);
        unlink_anon_vmas(new);
 out_free_mpol:
        mpol_put(vma_policy(new));
 out_free_vma:
        vm_area_free(new);
        return err;
}

/*
 * Split a vma into two pieces at address 'addr', a new vma is allocated
 * either for the first part or the tail.
 */
int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
              unsigned long addr, int new_below)
{
        if (mm->map_count >= sysctl_max_map_count)
                return -ENOMEM;

        return __split_vma(mm, vma, addr, new_below);
}

static inline void
unlock_range(struct vm_area_struct *start, unsigned long limit)
{
        struct mm_struct *mm = start->vm_mm;
        struct vm_area_struct *tmp = start;

        while (tmp && tmp->vm_start < limit) {
                if (tmp->vm_flags & VM_LOCKED) {
                        mm->locked_vm -= vma_pages(tmp);
                        munlock_vma_pages_all(tmp);
                }

                tmp = tmp->vm_next;
        }
}

/* Munmap is split into 2 main parts -- this part which finds
 * what needs doing, and the areas themselves, which do the
 * work.  This now handles partial unmappings.
 * Jeremy Fitzhardinge <jeremy@goop.org>
 */
int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
                struct list_head *uf, bool downgrade)
{
        unsigned long end;
        struct vm_area_struct *vma, *prev, *last;

        if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE-start)
                return -EINVAL;

        len = PAGE_ALIGN(len);
        end = start + len;
        if (len == 0)
                return -EINVAL;

        /*
         * arch_unmap() might do unmaps itself.  It must be called
         * and finish any rbtree manipulation before this code
         * runs and also starts to manipulate the rbtree.
         */
        arch_unmap(mm, start, end);

        /* Find the first overlapping VMA where start < vma->vm_end */
        vma = find_vma_intersection(mm, start, end);
        if (!vma)
                return 0;
        prev = vma->vm_prev;

        /*
         * If we need to split any vma, do it now to save pain later.
         *
         * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
         * unmapped vm_area_struct will remain in use: so lower split_vma
         * places tmp vma above, and higher split_vma places tmp vma below.
         */
        if (start > vma->vm_start) {
                int error;

                /*
                 * Make sure that map_count on return from munmap() will
                 * not exceed its limit; but let map_count go just above
                 * its limit temporarily, to help free resources as expected.
                 */
                if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
                        return -ENOMEM;

                error = __split_vma(mm, vma, start, 0);
                if (error)
                        return error;
                prev = vma;
        }

        /* Does it split the last one? */
        last = find_vma(mm, end);
        if (last && end > last->vm_start) {
                int error = __split_vma(mm, last, end, 1);
                if (error)
                        return error;
        }
        vma = vma_next(mm, prev);

        if (unlikely(uf)) {
                /*
                 * If userfaultfd_unmap_prep returns an error the vmas
                 * will remain split, but userland will get a
                 * highly unexpected error anyway. This is no
                 * different than the case where the first of the two
                 * __split_vma fails, but we don't undo the first
                 * split, despite we could. This is unlikely enough
                 * failure that it's not worth optimizing it for.
                 */
                int error = userfaultfd_unmap_prep(vma, start, end, uf);
                if (error)
                        return error;
        }

        /*
         * unlock any mlock()ed ranges before detaching vmas
         */
        if (mm->locked_vm)
                unlock_range(vma, end);

        /* Detach vmas from rbtree */
        if (!detach_vmas_to_be_unmapped(mm, vma, prev, end))
                downgrade = false;

        if (downgrade)
                mmap_write_downgrade(mm);

        unmap_region(mm, vma, prev, start, end);

        /* Fix up all other VM information */
        remove_vma_list(mm, vma);

        return downgrade ? 1 : 0;
}

int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
              struct list_head *uf)
{
        return __do_munmap(mm, start, len, uf, false);
}

static int __vm_munmap(unsigned long start, size_t len, bool downgrade)
{
        int ret;
        struct mm_struct *mm = current->mm;
        LIST_HEAD(uf);

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        ret = __do_munmap(mm, start, len, &uf, downgrade);
        /*
         * Returning 1 indicates mmap_lock is downgraded.
         * But 1 is not legal return value of vm_munmap() and munmap(), reset
         * it to 0 before return.
         */
        if (ret == 1) {
                mmap_read_unlock(mm);
                ret = 0;
        } else
                mmap_write_unlock(mm);

        userfaultfd_unmap_complete(mm, &uf);
        return ret;
}

int vm_munmap(unsigned long start, size_t len)
{
        return __vm_munmap(start, len, false);
}
EXPORT_SYMBOL(vm_munmap);

SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
{
        addr = untagged_addr(addr);
        profile_munmap(addr);
        return __vm_munmap(addr, len, true);
}


/*
 * Emulation of deprecated remap_file_pages() syscall.
 */
SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
                unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
{

        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long populate = 0;
        unsigned long ret = -EINVAL;
        struct file *file;

        pr_warn_once("%s (%d) uses deprecated remap_file_pages() syscall. See Documentation/vm/remap_file_pages.rst.\n",
                     current->comm, current->pid);

        if (prot)
                return ret;
        start = start & PAGE_MASK;
        size = size & PAGE_MASK;

        if (start + size <= start)
                return ret;

        /* Does pgoff wrap? */
        if (pgoff + (size >> PAGE_SHIFT) < pgoff)
                return ret;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        vma = vma_lookup(mm, start);

        if (!vma || !(vma->vm_flags & VM_SHARED))
                goto out;

        if (start + size > vma->vm_end) {
                struct vm_area_struct *next;

                for (next = vma->vm_next; next; next = next->vm_next) {
                        /* hole between vmas ? */
                        if (next->vm_start != next->vm_prev->vm_end)
                                goto out;

                        if (next->vm_file != vma->vm_file)
                                goto out;

                        if (next->vm_flags != vma->vm_flags)
                                goto out;

                        if (start + size <= next->vm_end)
                                break;
                }

                if (!next)
                        goto out;
        }

        prot |= vma->vm_flags & VM_READ ? PROT_READ : 0;
        prot |= vma->vm_flags & VM_WRITE ? PROT_WRITE : 0;
        prot |= vma->vm_flags & VM_EXEC ? PROT_EXEC : 0;

        flags &= MAP_NONBLOCK;
        flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE;
        if (vma->vm_flags & VM_LOCKED)
                flags |= MAP_LOCKED;

        file = get_file(vma->vm_file);
        ret = do_mmap(vma->vm_file, start, size,
                        prot, flags, pgoff, &populate, NULL);
        fput(file);
out:
        mmap_write_unlock(mm);
        if (populate)
                mm_populate(ret, populate);
        if (!IS_ERR_VALUE(ret))
                ret = 0;
        return ret;
}

/*
 *  this is really a simplified "do_mmap".  it only handles
 *  anonymous maps.  eventually we may be able to do some
 *  brk-specific accounting here.
 */
static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long flags, struct list_head *uf)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma, *prev;
        struct rb_node **rb_link, *rb_parent;
        pgoff_t pgoff = addr >> PAGE_SHIFT;
        int error;
        unsigned long mapped_addr;

        /* Until we need other flags, refuse anything except VM_EXEC. */
        if ((flags & (~VM_EXEC)) != 0)
                return -EINVAL;
        flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;

        mapped_addr = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
        if (IS_ERR_VALUE(mapped_addr))
                return mapped_addr;

        error = mlock_future_check(mm, mm->def_flags, len);
        if (error)
                return error;

        /* Clear old maps, set up prev, rb_link, rb_parent, and uf */
        if (munmap_vma_range(mm, addr, len, &prev, &rb_link, &rb_parent, uf))
                return -ENOMEM;

        /* Check against address space limits *after* clearing old maps... */
        if (!may_expand_vm(mm, flags, len >> PAGE_SHIFT))
                return -ENOMEM;

        if (mm->map_count > sysctl_max_map_count)
                return -ENOMEM;

        if (security_vm_enough_memory_mm(mm, len >> PAGE_SHIFT))
                return -ENOMEM;

        /* Can we just expand an old private anonymous mapping? */
        vma = vma_merge(mm, prev, addr, addr + len, flags,
                        NULL, NULL, pgoff, NULL, NULL_VM_UFFD_CTX);
        if (vma)
                goto out;

        /*
         * create a vma struct for an anonymous mapping
         */
        vma = vm_area_alloc(mm);
        if (!vma) {
                vm_unacct_memory(len >> PAGE_SHIFT);
                return -ENOMEM;
        }

        vma_set_anonymous(vma);
        vma->vm_start = addr;
        vma->vm_end = addr + len;
        vma->vm_pgoff = pgoff;
        vma->vm_flags = flags;
        vma->vm_page_prot = vm_get_page_prot(flags);
        vma_link(mm, vma, prev, rb_link, rb_parent);
out:
        perf_event_mmap(vma);
        mm->total_vm += len >> PAGE_SHIFT;
        mm->data_vm += len >> PAGE_SHIFT;
        if (flags & VM_LOCKED)
                mm->locked_vm += (len >> PAGE_SHIFT);
        vma->vm_flags |= VM_SOFTDIRTY;
        return 0;
}

int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        unsigned long len;
        int ret;
        bool populate;
        LIST_HEAD(uf);

        len = PAGE_ALIGN(request);
        if (len < request)
                return -ENOMEM;
        if (!len)
                return 0;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        ret = do_brk_flags(addr, len, flags, &uf);
        populate = ((mm->def_flags & VM_LOCKED) != 0);
        mmap_write_unlock(mm);
        userfaultfd_unmap_complete(mm, &uf);
        if (populate && !ret)
                mm_populate(addr, len);
        return ret;
}
EXPORT_SYMBOL(vm_brk_flags);

int vm_brk(unsigned long addr, unsigned long len)
{
        return vm_brk_flags(addr, len, 0);
}
EXPORT_SYMBOL(vm_brk);

/* Release all mmaps. */
void exit_mmap(struct mm_struct *mm)
{
        struct mmu_gather tlb;
        struct vm_area_struct *vma;
        unsigned long nr_accounted = 0;

        /* mm's last user has gone, and its about to be pulled down */
        mmu_notifier_release(mm);

        if (unlikely(mm_is_oom_victim(mm))) {
                /*
                 * Manually reap the mm to free as much memory as possible.
                 * Then, as the oom reaper does, set MMF_OOM_SKIP to disregard
                 * this mm from further consideration.  Taking mm->mmap_lock for
                 * write after setting MMF_OOM_SKIP will guarantee that the oom
                 * reaper will not run on this mm again after mmap_lock is
                 * dropped.
                 *
                 * Nothing can be holding mm->mmap_lock here and the above call
                 * to mmu_notifier_release(mm) ensures mmu notifier callbacks in
                 * __oom_reap_task_mm() will not block.
                 *
                 * This needs to be done before calling munlock_vma_pages_all(),
                 * which clears VM_LOCKED, otherwise the oom reaper cannot
                 * reliably test it.
                 */
                (void)__oom_reap_task_mm(mm);

                set_bit(MMF_OOM_SKIP, &mm->flags);
                mmap_write_lock(mm);
                mmap_write_unlock(mm);
        }

        if (mm->locked_vm)
                unlock_range(mm->mmap, ULONG_MAX);

        arch_exit_mmap(mm);

        vma = mm->mmap;
        if (!vma)       /* Can happen if dup_mmap() received an OOM */
                return;

        lru_add_drain();
        flush_cache_mm(mm);
        tlb_gather_mmu_fullmm(&tlb, mm);
        /* update_hiwater_rss(mm) here? but nobody should be looking */
        /* Use -1 here to ensure all VMAs in the mm are unmapped */
        unmap_vmas(&tlb, vma, 0, -1);
        free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
        tlb_finish_mmu(&tlb);

        /*
         * Walk the list again, actually closing and freeing it,
         * with preemption enabled, without holding any MM locks.
         */
        while (vma) {
                if (vma->vm_flags & VM_ACCOUNT)
                        nr_accounted += vma_pages(vma);
                vma = remove_vma(vma);
                cond_resched();
        }
        vm_unacct_memory(nr_accounted);
}

/* Insert vm structure into process list sorted by address
 * and into the inode's i_mmap tree.  If vm_file is non-NULL
 * then i_mmap_rwsem is taken here.
 */
int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
{
        struct vm_area_struct *prev;
        struct rb_node **rb_link, *rb_parent;

        if (find_vma_links(mm, vma->vm_start, vma->vm_end,
                           &prev, &rb_link, &rb_parent))
                return -ENOMEM;
        if ((vma->vm_flags & VM_ACCOUNT) &&
             security_vm_enough_memory_mm(mm, vma_pages(vma)))
                return -ENOMEM;

        /*
         * The vm_pgoff of a purely anonymous vma should be irrelevant
         * until its first write fault, when page's anon_vma and index
         * are set.  But now set the vm_pgoff it will almost certainly
         * end up with (unless mremap moves it elsewhere before that
         * first wfault), so /proc/pid/maps tells a consistent story.
         *
         * By setting it to reflect the virtual start address of the
         * vma, merges and splits can happen in a seamless way, just
         * using the existing file pgoff checks and manipulations.
         * Similarly in do_mmap and in do_brk_flags.
         */
        if (vma_is_anonymous(vma)) {
                BUG_ON(vma->anon_vma);
                vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
        }

        vma_link(mm, vma, prev, rb_link, rb_parent);
        return 0;
}

/*
 * Copy the vma structure to a new location in the same mm,
 * prior to moving page table entries, to effect an mremap move.
 */
struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
        unsigned long addr, unsigned long len, pgoff_t pgoff,
        bool *need_rmap_locks)
{
        struct vm_area_struct *vma = *vmap;
        unsigned long vma_start = vma->vm_start;
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *new_vma, *prev;
        struct rb_node **rb_link, *rb_parent;
        bool faulted_in_anon_vma = true;

        /*
         * If anonymous vma has not yet been faulted, update new pgoff
         * to match new location, to increase its chance of merging.
         */
        if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) {
                pgoff = addr >> PAGE_SHIFT;
                faulted_in_anon_vma = false;
        }

        if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent))
                return NULL;    /* should never get here */
        new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
                            vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
                            vma->vm_userfaultfd_ctx);
        if (new_vma) {
                /*
                 * Source vma may have been merged into new_vma
                 */
                if (unlikely(vma_start >= new_vma->vm_start &&
                             vma_start < new_vma->vm_end)) {
                        /*
                         * The only way we can get a vma_merge with
                         * self during an mremap is if the vma hasn't
                         * been faulted in yet and we were allowed to
                         * reset the dst vma->vm_pgoff to the
                         * destination address of the mremap to allow
                         * the merge to happen. mremap must change the
                         * vm_pgoff linearity between src and dst vmas
                         * (in turn preventing a vma_merge) to be
                         * safe. It is only safe to keep the vm_pgoff
                         * linear if there are no pages mapped yet.
                         */
                        VM_BUG_ON_VMA(faulted_in_anon_vma, new_vma);
                        *vmap = vma = new_vma;
                }
                *need_rmap_locks = (new_vma->vm_pgoff <= vma->vm_pgoff);
        } else {
                new_vma = vm_area_dup(vma);
                if (!new_vma)
                        goto out;
                new_vma->vm_start = addr;
                new_vma->vm_end = addr + len;
                new_vma->vm_pgoff = pgoff;
                if (vma_dup_policy(vma, new_vma))
                        goto out_free_vma;
                if (anon_vma_clone(new_vma, vma))
                        goto out_free_mempol;
                if (new_vma->vm_file)
                        get_file(new_vma->vm_file);
                if (new_vma->vm_ops && new_vma->vm_ops->open)
                        new_vma->vm_ops->open(new_vma);
                vma_link(mm, new_vma, prev, rb_link, rb_parent);
                *need_rmap_locks = false;
        }
        return new_vma;

out_free_mempol:
        mpol_put(vma_policy(new_vma));
out_free_vma:
        vm_area_free(new_vma);
out:
        return NULL;
}

/*
 * Return true if the calling process may expand its vm space by the passed
 * number of pages
 */
bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
{
        if (mm->total_vm + npages > rlimit(RLIMIT_AS) >> PAGE_SHIFT)
                return false;

        if (is_data_mapping(flags) &&
            mm->data_vm + npages > rlimit(RLIMIT_DATA) >> PAGE_SHIFT) {
                /* Workaround for Valgrind */
                if (rlimit(RLIMIT_DATA) == 0 &&
                    mm->data_vm + npages <= rlimit_max(RLIMIT_DATA) >> PAGE_SHIFT)
                        return true;

                pr_warn_once("%s (%d): VmData %lu exceed data ulimit %lu. Update limits%s.\n",
                             current->comm, current->pid,
                             (mm->data_vm + npages) << PAGE_SHIFT,
                             rlimit(RLIMIT_DATA),
                             ignore_rlimit_data ? "" : " or use boot option ignore_rlimit_data");

                if (!ignore_rlimit_data)
                        return false;
        }

        return true;
}

void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
{
        mm->total_vm += npages;

        if (is_exec_mapping(flags))
                mm->exec_vm += npages;
        else if (is_stack_mapping(flags))
                mm->stack_vm += npages;
        else if (is_data_mapping(flags))
                mm->data_vm += npages;
}

static vm_fault_t special_mapping_fault(struct vm_fault *vmf);

/*
 * Having a close hook prevents vma merging regardless of flags.
 */
static void special_mapping_close(struct vm_area_struct *vma)
{
}

static const char *special_mapping_name(struct vm_area_struct *vma)
{
        return ((struct vm_special_mapping *)vma->vm_private_data)->name;
}

static int special_mapping_mremap(struct vm_area_struct *new_vma)
{
        struct vm_special_mapping *sm = new_vma->vm_private_data;

        if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
                return -EFAULT;

        if (sm->mremap)
                return sm->mremap(sm, new_vma);

        return 0;
}

static int special_mapping_split(struct vm_area_struct *vma, unsigned long addr)
{
        /*
         * Forbid splitting special mappings - kernel has expectations over
         * the number of pages in mapping. Together with VM_DONTEXPAND
         * the size of vma should stay the same over the special mapping's
         * lifetime.
         */
        return -EINVAL;
}

static const struct vm_operations_struct special_mapping_vmops = {
        .close = special_mapping_close,
        .fault = special_mapping_fault,
        .mremap = special_mapping_mremap,
        .name = special_mapping_name,
        /* vDSO code relies that VVAR can't be accessed remotely */
        .access = NULL,
        .may_split = special_mapping_split,
};

static const struct vm_operations_struct legacy_special_mapping_vmops = {
        .close = special_mapping_close,
        .fault = special_mapping_fault,
};

static vm_fault_t special_mapping_fault(struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        pgoff_t pgoff;
        struct page **pages;

        if (vma->vm_ops == &legacy_special_mapping_vmops) {
                pages = vma->vm_private_data;
        } else {
                struct vm_special_mapping *sm = vma->vm_private_data;

                if (sm->fault)
                        return sm->fault(sm, vmf->vma, vmf);

                pages = sm->pages;
        }

        for (pgoff = vmf->pgoff; pgoff && *pages; ++pages)
                pgoff--;

        if (*pages) {
                struct page *page = *pages;
                get_page(page);
                vmf->page = page;
                return 0;
        }

        return VM_FAULT_SIGBUS;
}

static struct vm_area_struct *__install_special_mapping(
        struct mm_struct *mm,
        unsigned long addr, unsigned long len,
        unsigned long vm_flags, void *priv,
        const struct vm_operations_struct *ops)
{
        int ret;
        struct vm_area_struct *vma;

        vma = vm_area_alloc(mm);
        if (unlikely(vma == NULL))
                return ERR_PTR(-ENOMEM);

        vma->vm_start = addr;
        vma->vm_end = addr + len;

        vma->vm_flags = vm_flags | mm->def_flags | VM_DONTEXPAND | VM_SOFTDIRTY;
        vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);

        vma->vm_ops = ops;
        vma->vm_private_data = priv;

        ret = insert_vm_struct(mm, vma);
        if (ret)
                goto out;

        vm_stat_account(mm, vma->vm_flags, len >> PAGE_SHIFT);

        perf_event_mmap(vma);

        return vma;

out:
        vm_area_free(vma);
        return ERR_PTR(ret);
}

bool vma_is_special_mapping(const struct vm_area_struct *vma,
        const struct vm_special_mapping *sm)
{
        return vma->vm_private_data == sm &&
                (vma->vm_ops == &special_mapping_vmops ||
                 vma->vm_ops == &legacy_special_mapping_vmops);
}

/*
 * Called with mm->mmap_lock held for writing.
 * Insert a new vma covering the given region, with the given flags.
 * Its pages are supplied by the given array of struct page *.
 * The array can be shorter than len >> PAGE_SHIFT if it's null-terminated.
 * The region past the last page supplied will always produce SIGBUS.
 * The array pointer and the pages it points to are assumed to stay alive
 * for as long as this mapping might exist.
 */
struct vm_area_struct *_install_special_mapping(
        struct mm_struct *mm,
        unsigned long addr, unsigned long len,
        unsigned long vm_flags, const struct vm_special_mapping *spec)
{
        return __install_special_mapping(mm, addr, len, vm_flags, (void *)spec,
                                        &special_mapping_vmops);
}

int install_special_mapping(struct mm_struct *mm,
                            unsigned long addr, unsigned long len,
                            unsigned long vm_flags, struct page **pages)
{
        struct vm_area_struct *vma = __install_special_mapping(
                mm, addr, len, vm_flags, (void *)pages,
                &legacy_special_mapping_vmops);

        return PTR_ERR_OR_ZERO(vma);
}

static DEFINE_MUTEX(mm_all_locks_mutex);

static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)
{
        if (!test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_root.rb_node)) {
                /*
                 * The LSB of head.next can't change from under us
                 * because we hold the mm_all_locks_mutex.
                 */
                down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_lock);
                /*
                 * We can safely modify head.next after taking the
                 * anon_vma->root->rwsem. If some other vma in this mm shares
                 * the same anon_vma we won't take it again.
                 *
                 * No need of atomic instructions here, head.next
                 * can't change from under us thanks to the
                 * anon_vma->root->rwsem.
                 */
                if (__test_and_set_bit(0, (unsigned long *)
                                       &anon_vma->root->rb_root.rb_root.rb_node))
                        BUG();
        }
}

static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
{
        if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
                /*
                 * AS_MM_ALL_LOCKS can't change from under us because
                 * we hold the mm_all_locks_mutex.
                 *
                 * Operations on ->flags have to be atomic because
                 * even if AS_MM_ALL_LOCKS is stable thanks to the
                 * mm_all_locks_mutex, there may be other cpus
                 * changing other bitflags in parallel to us.
                 */
                if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
                        BUG();
                down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_lock);
        }
}

/*
 * This operation locks against the VM for all pte/vma/mm related
 * operations that could ever happen on a certain mm. This includes
 * vmtruncate, try_to_unmap, and all page faults.
 *
 * The caller must take the mmap_lock in write mode before calling
 * mm_take_all_locks(). The caller isn't allowed to release the
 * mmap_lock until mm_drop_all_locks() returns.
 *
 * mmap_lock in write mode is required in order to block all operations
 * that could modify pagetables and free pages without need of
 * altering the vma layout. It's also needed in write mode to avoid new
 * anon_vmas to be associated with existing vmas.
 *
 * A single task can't take more than one mm_take_all_locks() in a row
 * or it would deadlock.
 *
 * The LSB in anon_vma->rb_root.rb_node and the AS_MM_ALL_LOCKS bitflag in
 * mapping->flags avoid to take the same lock twice, if more than one
 * vma in this mm is backed by the same anon_vma or address_space.
 *
 * We take locks in following order, accordingly to comment at beginning
 * of mm/rmap.c:
 *   - all hugetlbfs_i_mmap_rwsem_key locks (aka mapping->i_mmap_rwsem for
 *     hugetlb mapping);
 *   - all i_mmap_rwsem locks;
 *   - all anon_vma->rwseml
 *
 * We can take all locks within these types randomly because the VM code
 * doesn't nest them and we protected from parallel mm_take_all_locks() by
 * mm_all_locks_mutex.
 *
 * mm_take_all_locks() and mm_drop_all_locks are expensive operations
 * that may have to take thousand of locks.
 *
 * mm_take_all_locks() can fail if it's interrupted by signals.
 */
int mm_take_all_locks(struct mm_struct *mm)
{
        struct vm_area_struct *vma;
        struct anon_vma_chain *avc;

        BUG_ON(mmap_read_trylock(mm));

        mutex_lock(&mm_all_locks_mutex);

        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->vm_file && vma->vm_file->f_mapping &&
                                is_vm_hugetlb_page(vma))
                        vm_lock_mapping(mm, vma->vm_file->f_mapping);
        }

        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->vm_file && vma->vm_file->f_mapping &&
                                !is_vm_hugetlb_page(vma))
                        vm_lock_mapping(mm, vma->vm_file->f_mapping);
        }

        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->anon_vma)
                        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                                vm_lock_anon_vma(mm, avc->anon_vma);
        }

        return 0;

out_unlock:
        mm_drop_all_locks(mm);
        return -EINTR;
}

static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
{
        if (test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_root.rb_node)) {
                /*
                 * The LSB of head.next can't change to 0 from under
                 * us because we hold the mm_all_locks_mutex.
                 *
                 * We must however clear the bitflag before unlocking
                 * the vma so the users using the anon_vma->rb_root will
                 * never see our bitflag.
                 *
                 * No need of atomic instructions here, head.next
                 * can't change from under us until we release the
                 * anon_vma->root->rwsem.
                 */
                if (!__test_and_clear_bit(0, (unsigned long *)
                                          &anon_vma->root->rb_root.rb_root.rb_node))
                        BUG();
                anon_vma_unlock_write(anon_vma);
        }
}

static void vm_unlock_mapping(struct address_space *mapping)
{
        if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
                /*
                 * AS_MM_ALL_LOCKS can't change to 0 from under us
                 * because we hold the mm_all_locks_mutex.
                 */
                i_mmap_unlock_write(mapping);
                if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
                                        &mapping->flags))
                        BUG();
        }
}

/*
 * The mmap_lock cannot be released by the caller until
 * mm_drop_all_locks() returns.
 */
void mm_drop_all_locks(struct mm_struct *mm)
{
        struct vm_area_struct *vma;
        struct anon_vma_chain *avc;

        BUG_ON(mmap_read_trylock(mm));
        BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));

        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                if (vma->anon_vma)
                        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                                vm_unlock_anon_vma(avc->anon_vma);
                if (vma->vm_file && vma->vm_file->f_mapping)
                        vm_unlock_mapping(vma->vm_file->f_mapping);
        }

        mutex_unlock(&mm_all_locks_mutex);
}

/*
 * initialise the percpu counter for VM
 */
void __init mmap_init(void)
{
        int ret;

        ret = percpu_counter_init(&vm_committed_as, 0, GFP_KERNEL);
        VM_BUG_ON(ret);
}

/*
 * Initialise sysctl_user_reserve_kbytes.
 *
 * This is intended to prevent a user from starting a single memory hogging
 * process, such that they cannot recover (kill the hog) in OVERCOMMIT_NEVER
 * mode.
 *
 * The default value is min(3% of free memory, 128MB)
 * 128MB is enough to recover with sshd/login, bash, and top/kill.
 */
static int init_user_reserve(void)
{
        unsigned long free_kbytes;

        free_kbytes = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);

        sysctl_user_reserve_kbytes = min(free_kbytes / 32, 1UL << 17);
        return 0;
}
subsys_initcall(init_user_reserve);

/*
 * Initialise sysctl_admin_reserve_kbytes.
 *
 * The purpose of sysctl_admin_reserve_kbytes is to allow the sys admin
 * to log in and kill a memory hogging process.
 *
 * Systems with more than 256MB will reserve 8MB, enough to recover
 * with sshd, bash, and top in OVERCOMMIT_GUESS. Smaller systems will
 * only reserve 3% of free pages by default.
 */
static int init_admin_reserve(void)
{
        unsigned long free_kbytes;

        free_kbytes = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);

        sysctl_admin_reserve_kbytes = min(free_kbytes / 32, 1UL << 13);
        return 0;
}
subsys_initcall(init_admin_reserve);

/*
 * Reinititalise user and admin reserves if memory is added or removed.
 *
 * The default user reserve max is 128MB, and the default max for the
 * admin reserve is 8MB. These are usually, but not always, enough to
 * enable recovery from a memory hogging process using login/sshd, a shell,
 * and tools like top. It may make sense to increase or even disable the
 * reserve depending on the existence of swap or variations in the recovery
 * tools. So, the admin may have changed them.
 *
 * If memory is added and the reserves have been eliminated or increased above
 * the default max, then we'll trust the admin.
 *
 * If memory is removed and there isn't enough free memory, then we
 * need to reset the reserves.
 *
 * Otherwise keep the reserve set by the admin.
 */
static int reserve_mem_notifier(struct notifier_block *nb,
                             unsigned long action, void *data)
{
        unsigned long tmp, free_kbytes;

        switch (action) {
        case MEM_ONLINE:
                /* Default max is 128MB. Leave alone if modified by operator. */
                tmp = sysctl_user_reserve_kbytes;
                if (0 < tmp && tmp < (1UL << 17))
                        init_user_reserve();

                /* Default max is 8MB.  Leave alone if modified by operator. */
                tmp = sysctl_admin_reserve_kbytes;
                if (0 < tmp && tmp < (1UL << 13))
                        init_admin_reserve();

                break;
        case MEM_OFFLINE:
                free_kbytes = global_zone_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);

                if (sysctl_user_reserve_kbytes > free_kbytes) {
                        init_user_reserve();
                        pr_info("vm.user_reserve_kbytes reset to %lu\n",
                                sysctl_user_reserve_kbytes);
                }

                if (sysctl_admin_reserve_kbytes > free_kbytes) {
                        init_admin_reserve();
                        pr_info("vm.admin_reserve_kbytes reset to %lu\n",
                                sysctl_admin_reserve_kbytes);
                }
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block reserve_mem_nb = {
        .notifier_call = reserve_mem_notifier,
};

static int __meminit init_reserve_notifier(void)
{
        if (register_hotmemory_notifier(&reserve_mem_nb))
                pr_err("Failed registering memory add/remove notifier for admin reserve\n");

        return 0;
}
subsys_initcall(init_reserve_notifier);