mm/fremap.c

   1 /*
   2  *   linux/mm/fremap.c
   3  *
   4  * Explicit pagetable population and nonlinear (random) mappings support.
   5  *
   6  * started by Ingo Molnar, Copyright (C) 2002, 2003
   7  */
   8 #include <linux/export.h>
   9 #include <linux/backing-dev.h>
  10 #include <linux/mm.h>
  11 #include <linux/swap.h>
  12 #include <linux/file.h>
  13 #include <linux/mman.h>
  14 #include <linux/pagemap.h>
  15 #include <linux/swapops.h>
  16 #include <linux/rmap.h>
  17 #include <linux/syscalls.h>
  18 #include <linux/mmu_notifier.h>
  19
  20 #include <asm/mmu_context.h>
  21 #include <asm/cacheflush.h>
  22 #include <asm/tlbflush.h>
  23
  24 #include "internal.h"
  25
  26 static int mm_counter(struct page *page)
  27 {
  28         return PageAnon(page) ? MM_ANONPAGES : MM_FILEPAGES;
  29 }
  30
  31 static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  32                         unsigned long addr, pte_t *ptep)
  33 {
  34         pte_t pte = *ptep;
  35         struct page *page;
  36         swp_entry_t entry;
  37
  38         if (pte_present(pte)) {
  39                 flush_cache_page(vma, addr, pte_pfn(pte));
  40                 pte = ptep_clear_flush(vma, addr, ptep);
  41                 page = vm_normal_page(vma, addr, pte);
  42                 if (page) {
  43                         if (pte_dirty(pte))
  44                                 set_page_dirty(page);
  45                         update_hiwater_rss(mm);
  46                         dec_mm_counter(mm, mm_counter(page));
  47                         page_remove_rmap(page);
  48                         page_cache_release(page);
  49                 }
  50         } else {        /* zap_pte() is not called when pte_none() */
  51                 if (!pte_file(pte)) {
  52                         update_hiwater_rss(mm);
  53                         entry = pte_to_swp_entry(pte);
  54                         if (non_swap_entry(entry)) {
  55                                 if (is_migration_entry(entry)) {
  56                                         page = migration_entry_to_page(entry);
  57                                         dec_mm_counter(mm, mm_counter(page));
  58                                 }
  59                         } else {
  60                                 free_swap_and_cache(entry);
  61                                 dec_mm_counter(mm, MM_SWAPENTS);
  62                         }
  63                 }
  64                 pte_clear_not_present_full(mm, addr, ptep, 0);
  65         }
  66 }
  67
  68 /*
  69  * Install a file pte to a given virtual memory address, release any
  70  * previously existing mapping.
  71  */
  72 static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
  73                 unsigned long addr, unsigned long pgoff, pgprot_t prot)
  74 {
  75         int err = -ENOMEM;
  76         pte_t *pte, ptfile;
  77         spinlock_t *ptl;
  78
  79         pte = get_locked_pte(mm, addr, &ptl);
  80         if (!pte)
  81                 goto out;
  82
  83         ptfile = pgoff_to_pte(pgoff);
  84
  85         if (!pte_none(*pte)) {
  86                 if (pte_present(*pte) && pte_soft_dirty(*pte))
  87                         pte_file_mksoft_dirty(ptfile);
  88                 zap_pte(mm, vma, addr, pte);
  89         }
  90
  91         set_pte_at(mm, addr, pte, ptfile);
  92         /*
  93          * We don't need to run update_mmu_cache() here because the "file pte"
  94          * being installed by install_file_pte() is not a real pte - it's a
  95          * non-present entry (like a swap entry), noting what file offset should
  96          * be mapped there when there's a fault (in a non-linear vma where
  97          * that's not obvious).
  98          */
  99         pte_unmap_unlock(pte, ptl);
 100         err = 0;
 101 out:
 102         return err;
 103 }
 104
 105 int generic_file_remap_pages(struct vm_area_struct *vma, unsigned long addr,
 106                              unsigned long size, pgoff_t pgoff)
 107 {
 108         struct mm_struct *mm = vma->vm_mm;
 109         int err;
 110
 111         do {
 112                 err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
 113                 if (err)
 114                         return err;
 115
 116                 size -= PAGE_SIZE;
 117                 addr += PAGE_SIZE;
 118                 pgoff++;
 119         } while (size);
 120
 121         return 0;
 122 }
 123 EXPORT_SYMBOL(generic_file_remap_pages);
 124
 125 /**
 126  * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
 127  * @start: start of the remapped virtual memory range
 128  * @size: size of the remapped virtual memory range
 129  * @prot: new protection bits of the range (see NOTE)
 130  * @pgoff: to-be-mapped page of the backing store file
 131  * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 132  *
 133  * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
 134  * (shared backing store file).
 135  *
 136  * This syscall works purely via pagetables, so it's the most efficient
 137  * way to map the same (large) file into a given virtual window. Unlike
 138  * mmap()/mremap() it does not create any new vmas. The new mappings are
 139  * also safe across swapout.
 140  *
 141  * NOTE: the @prot parameter right now is ignored (but must be zero),
 142  * and the vma's default protection is used. Arbitrary protections
 143  * might be implemented in the future.
 144  */
 145 SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 146                 unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
 147 {
 148         struct mm_struct *mm = current->mm;
 149         struct address_space *mapping;
 150         struct vm_area_struct *vma;
 151         int err = -EINVAL;
 152         int has_write_lock = 0;
 153         vm_flags_t vm_flags = 0;
 154
 155         if (prot)
 156                 return err;
 157         /*
 158          * Sanitize the syscall parameters:
 159          */
 160         start = start & PAGE_MASK;
 161         size = size & PAGE_MASK;
 162
 163         /* Does the address range wrap, or is the span zero-sized? */
 164         if (start + size <= start)
 165                 return err;
 166
 167         /* Does pgoff wrap? */
 168         if (pgoff + (size >> PAGE_SHIFT) < pgoff)
 169                 return err;
 170
 171         /* Can we represent this offset inside this architecture's pte's? */
 172 #if PTE_FILE_MAX_BITS < BITS_PER_LONG
 173         if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
 174                 return err;
 175 #endif
 176
 177         /* We need down_write() to change vma->vm_flags. */
 178         down_read(&mm->mmap_sem);
 179  retry:
 180         vma = find_vma(mm, start);
 181
 182         /*
 183          * Make sure the vma is shared, that it supports prefaulting,
 184          * and that the remapped range is valid and fully within
 185          * the single existing vma.
 186          */
 187         if (!vma || !(vma->vm_flags & VM_SHARED))
 188                 goto out;
 189
 190         if (!vma->vm_ops || !vma->vm_ops->remap_pages)
 191                 goto out;
 192
 193         if (start < vma->vm_start || start + size > vma->vm_end)
 194                 goto out;
 195
 196         /* Must set VM_NONLINEAR before any pages are populated. */
 197         if (!(vma->vm_flags & VM_NONLINEAR)) {
 198                 /*
 199                  * vm_private_data is used as a swapout cursor
 200                  * in a VM_NONLINEAR vma.
 201                  */
 202                 if (vma->vm_private_data)
 203                         goto out;
 204
 205                 /* Don't need a nonlinear mapping, exit success */
 206                 if (pgoff == linear_page_index(vma, start)) {
 207                         err = 0;
 208                         goto out;
 209                 }
 210
 211                 if (!has_write_lock) {
 212 get_write_lock:
 213                         up_read(&mm->mmap_sem);
 214                         down_write(&mm->mmap_sem);
 215                         has_write_lock = 1;
 216                         goto retry;
 217                 }
 218                 mapping = vma->vm_file->f_mapping;
 219                 /*
 220                  * page_mkclean doesn't work on nonlinear vmas, so if
 221                  * dirty pages need to be accounted, emulate with linear
 222                  * vmas.
 223                  */
 224                 if (mapping_cap_account_dirty(mapping)) {
 225                         unsigned long addr;
 226                         struct file *file = get_file(vma->vm_file);
 227                         /* mmap_region may free vma; grab the info now */
 228                         vm_flags = vma->vm_flags;
 229
 230                         addr = mmap_region(file, start, size, vm_flags, pgoff);
 231                         fput(file);
 232                         if (IS_ERR_VALUE(addr)) {
 233                                 err = addr;
 234                         } else {
 235                                 BUG_ON(addr != start);
 236                                 err = 0;
 237                         }
 238                         goto out_freed;
 239                 }
 240                 mutex_lock(&mapping->i_mmap_mutex);
 241                 flush_dcache_mmap_lock(mapping);
 242                 vma->vm_flags |= VM_NONLINEAR;
 243                 vma_interval_tree_remove(vma, &mapping->i_mmap);
 244                 vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
 245                 flush_dcache_mmap_unlock(mapping);
 246                 mutex_unlock(&mapping->i_mmap_mutex);
 247         }
 248
 249         if (vma->vm_flags & VM_LOCKED) {
 250                 /*
 251                  * drop PG_Mlocked flag for over-mapped range
 252                  */
 253                 if (!has_write_lock)
 254                         goto get_write_lock;
 255                 vm_flags = vma->vm_flags;
 256                 munlock_vma_pages_range(vma, start, start + size);
 257                 vma->vm_flags = vm_flags;
 258         }
 259
 260         mmu_notifier_invalidate_range_start(mm, start, start + size);
 261         err = vma->vm_ops->remap_pages(vma, start, size, pgoff);
 262         mmu_notifier_invalidate_range_end(mm, start, start + size);
 263
 264         /*
 265          * We can't clear VM_NONLINEAR because we'd have to do
 266          * it after ->populate completes, and that would prevent
 267          * downgrading the lock.  (Locks can't be upgraded).
 268          */
 269
 270 out:
 271         if (vma)
 272                 vm_flags = vma->vm_flags;
 273 out_freed:
 274         if (likely(!has_write_lock))
 275                 up_read(&mm->mmap_sem);
 276         else
 277                 up_write(&mm->mmap_sem);
 278         if (!err && ((vm_flags & VM_LOCKED) || !(flags & MAP_NONBLOCK)))
 279                 mm_populate(start, size);
 280
 281         return err;
 282 }