mm/mapping_dirty_helpers.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/pagewalk.h>
   3 #include <linux/hugetlb.h>
   4 #include <linux/bitops.h>
   5 #include <linux/mmu_notifier.h>
   6 #include <linux/mm_inline.h>
   7 #include <asm/cacheflush.h>
   8 #include <asm/tlbflush.h>
   9
  10 /**
  11  * struct wp_walk - Private struct for pagetable walk callbacks
  12  * @range: Range for mmu notifiers
  13  * @tlbflush_start: Address of first modified pte
  14  * @tlbflush_end: Address of last modified pte + 1
  15  * @total: Total number of modified ptes
  16  */
  17 struct wp_walk {
  18         struct mmu_notifier_range range;
  19         unsigned long tlbflush_start;
  20         unsigned long tlbflush_end;
  21         unsigned long total;
  22 };
  23
  24 /**
  25  * wp_pte - Write-protect a pte
  26  * @pte: Pointer to the pte
  27  * @addr: The start of protecting virtual address
  28  * @end: The end of protecting virtual address
  29  * @walk: pagetable walk callback argument
  30  *
  31  * The function write-protects a pte and records the range in
  32  * virtual address space of touched ptes for efficient range TLB flushes.
  33  */
  34 static int wp_pte(pte_t *pte, unsigned long addr, unsigned long end,
  35                   struct mm_walk *walk)
  36 {
  37         struct wp_walk *wpwalk = walk->private;
  38         pte_t ptent = *pte;
  39
  40         if (pte_write(ptent)) {
  41                 pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
  42
  43                 ptent = pte_wrprotect(old_pte);
  44                 ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
  45                 wpwalk->total++;
  46                 wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
  47                 wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
  48                                            addr + PAGE_SIZE);
  49         }
  50
  51         return 0;
  52 }
  53
  54 /**
  55  * struct clean_walk - Private struct for the clean_record_pte function.
  56  * @base: struct wp_walk we derive from
  57  * @bitmap_pgoff: Address_space Page offset of the first bit in @bitmap
  58  * @bitmap: Bitmap with one bit for each page offset in the address_space range
  59  * covered.
  60  * @start: Address_space page offset of first modified pte relative
  61  * to @bitmap_pgoff
  62  * @end: Address_space page offset of last modified pte relative
  63  * to @bitmap_pgoff
  64  */
  65 struct clean_walk {
  66         struct wp_walk base;
  67         pgoff_t bitmap_pgoff;
  68         unsigned long *bitmap;
  69         pgoff_t start;
  70         pgoff_t end;
  71 };
  72
  73 #define to_clean_walk(_wpwalk) container_of(_wpwalk, struct clean_walk, base)
  74
  75 /**
  76  * clean_record_pte - Clean a pte and record its address space offset in a
  77  * bitmap
  78  * @pte: Pointer to the pte
  79  * @addr: The start of virtual address to be clean
  80  * @end: The end of virtual address to be clean
  81  * @walk: pagetable walk callback argument
  82  *
  83  * The function cleans a pte and records the range in
  84  * virtual address space of touched ptes for efficient TLB flushes.
  85  * It also records dirty ptes in a bitmap representing page offsets
  86  * in the address_space, as well as the first and last of the bits
  87  * touched.
  88  */
  89 static int clean_record_pte(pte_t *pte, unsigned long addr,
  90                             unsigned long end, struct mm_walk *walk)
  91 {
  92         struct wp_walk *wpwalk = walk->private;
  93         struct clean_walk *cwalk = to_clean_walk(wpwalk);
  94         pte_t ptent = *pte;
  95
  96         if (pte_dirty(ptent)) {
  97                 pgoff_t pgoff = ((addr - walk->vma->vm_start) >> PAGE_SHIFT) +
  98                         walk->vma->vm_pgoff - cwalk->bitmap_pgoff;
  99                 pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
 100
 101                 ptent = pte_mkclean(old_pte);
 102                 ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
 103
 104                 wpwalk->total++;
 105                 wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
 106                 wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
 107                                            addr + PAGE_SIZE);
 108
 109                 __set_bit(pgoff, cwalk->bitmap);
 110                 cwalk->start = min(cwalk->start, pgoff);
 111                 cwalk->end = max(cwalk->end, pgoff + 1);
 112         }
 113
 114         return 0;
 115 }
 116
 117 /*
 118  * wp_clean_pmd_entry - The pagewalk pmd callback.
 119  *
 120  * Dirty-tracking should take place on the PTE level, so
 121  * WARN() if encountering a dirty huge pmd.
 122  * Furthermore, never split huge pmds, since that currently
 123  * causes dirty info loss. The pagefault handler should do
 124  * that if needed.
 125  */
 126 static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
 127                               struct mm_walk *walk)
 128 {
 129         pmd_t pmdval = pmdp_get_lockless(pmd);
 130
 131         if (!pmd_trans_unstable(&pmdval))
 132                 return 0;
 133
 134         if (pmd_none(pmdval)) {
 135                 walk->action = ACTION_AGAIN;
 136                 return 0;
 137         }
 138
 139         /* Huge pmd, present or migrated */
 140         walk->action = ACTION_CONTINUE;
 141         if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
 142                 WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));
 143
 144         return 0;
 145 }
 146
 147 /*
 148  * wp_clean_pud_entry - The pagewalk pud callback.
 149  *
 150  * Dirty-tracking should take place on the PTE level, so
 151  * WARN() if encountering a dirty huge puds.
 152  * Furthermore, never split huge puds, since that currently
 153  * causes dirty info loss. The pagefault handler should do
 154  * that if needed.
 155  */
 156 static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
 157                               struct mm_walk *walk)
 158 {
 159         pud_t pudval = READ_ONCE(*pud);
 160
 161         if (!pud_trans_unstable(&pudval))
 162                 return 0;
 163
 164         if (pud_none(pudval)) {
 165                 walk->action = ACTION_AGAIN;
 166                 return 0;
 167         }
 168
 169 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 170         /* Huge pud */
 171         walk->action = ACTION_CONTINUE;
 172         if (pud_trans_huge(pudval) || pud_devmap(pudval))
 173                 WARN_ON(pud_write(pudval) || pud_dirty(pudval));
 174 #endif
 175
 176         return 0;
 177 }
 178
 179 /*
 180  * wp_clean_pre_vma - The pagewalk pre_vma callback.
 181  *
 182  * The pre_vma callback performs the cache flush, stages the tlb flush
 183  * and calls the necessary mmu notifiers.
 184  */
 185 static int wp_clean_pre_vma(unsigned long start, unsigned long end,
 186                             struct mm_walk *walk)
 187 {
 188         struct wp_walk *wpwalk = walk->private;
 189
 190         wpwalk->tlbflush_start = end;
 191         wpwalk->tlbflush_end = start;
 192
 193         mmu_notifier_range_init(&wpwalk->range, MMU_NOTIFY_PROTECTION_PAGE, 0,
 194                                 walk->mm, start, end);
 195         mmu_notifier_invalidate_range_start(&wpwalk->range);
 196         flush_cache_range(walk->vma, start, end);
 197
 198         /*
 199          * We're not using tlb_gather_mmu() since typically
 200          * only a small subrange of PTEs are affected, whereas
 201          * tlb_gather_mmu() records the full range.
 202          */
 203         inc_tlb_flush_pending(walk->mm);
 204
 205         return 0;
 206 }
 207
 208 /*
 209  * wp_clean_post_vma - The pagewalk post_vma callback.
 210  *
 211  * The post_vma callback performs the tlb flush and calls necessary mmu
 212  * notifiers.
 213  */
 214 static void wp_clean_post_vma(struct mm_walk *walk)
 215 {
 216         struct wp_walk *wpwalk = walk->private;
 217
 218         if (mm_tlb_flush_nested(walk->mm))
 219                 flush_tlb_range(walk->vma, wpwalk->range.start,
 220                                 wpwalk->range.end);
 221         else if (wpwalk->tlbflush_end > wpwalk->tlbflush_start)
 222                 flush_tlb_range(walk->vma, wpwalk->tlbflush_start,
 223                                 wpwalk->tlbflush_end);
 224
 225         mmu_notifier_invalidate_range_end(&wpwalk->range);
 226         dec_tlb_flush_pending(walk->mm);
 227 }
 228
 229 /*
 230  * wp_clean_test_walk - The pagewalk test_walk callback.
 231  *
 232  * Won't perform dirty-tracking on COW, read-only or HUGETLB vmas.
 233  */
 234 static int wp_clean_test_walk(unsigned long start, unsigned long end,
 235                               struct mm_walk *walk)
 236 {
 237         unsigned long vm_flags = READ_ONCE(walk->vma->vm_flags);
 238
 239         /* Skip non-applicable VMAs */
 240         if ((vm_flags & (VM_SHARED | VM_MAYWRITE | VM_HUGETLB)) !=
 241             (VM_SHARED | VM_MAYWRITE))
 242                 return 1;
 243
 244         return 0;
 245 }
 246
 247 static const struct mm_walk_ops clean_walk_ops = {
 248         .pte_entry = clean_record_pte,
 249         .pmd_entry = wp_clean_pmd_entry,
 250         .pud_entry = wp_clean_pud_entry,
 251         .test_walk = wp_clean_test_walk,
 252         .pre_vma = wp_clean_pre_vma,
 253         .post_vma = wp_clean_post_vma
 254 };
 255
 256 static const struct mm_walk_ops wp_walk_ops = {
 257         .pte_entry = wp_pte,
 258         .pmd_entry = wp_clean_pmd_entry,
 259         .pud_entry = wp_clean_pud_entry,
 260         .test_walk = wp_clean_test_walk,
 261         .pre_vma = wp_clean_pre_vma,
 262         .post_vma = wp_clean_post_vma
 263 };
 264
 265 /**
 266  * wp_shared_mapping_range - Write-protect all ptes in an address space range
 267  * @mapping: The address_space we want to write protect
 268  * @first_index: The first page offset in the range
 269  * @nr: Number of incremental page offsets to cover
 270  *
 271  * Note: This function currently skips transhuge page-table entries, since
 272  * it's intended for dirty-tracking on the PTE level. It will warn on
 273  * encountering transhuge write-enabled entries, though, and can easily be
 274  * extended to handle them as well.
 275  *
 276  * Return: The number of ptes actually write-protected. Note that
 277  * already write-protected ptes are not counted.
 278  */
 279 unsigned long wp_shared_mapping_range(struct address_space *mapping,
 280                                       pgoff_t first_index, pgoff_t nr)
 281 {
 282         struct wp_walk wpwalk = { .total = 0 };
 283
 284         i_mmap_lock_read(mapping);
 285         WARN_ON(walk_page_mapping(mapping, first_index, nr, &wp_walk_ops,
 286                                   &wpwalk));
 287         i_mmap_unlock_read(mapping);
 288
 289         return wpwalk.total;
 290 }
 291 EXPORT_SYMBOL_GPL(wp_shared_mapping_range);
 292
 293 /**
 294  * clean_record_shared_mapping_range - Clean and record all ptes in an
 295  * address space range
 296  * @mapping: The address_space we want to clean
 297  * @first_index: The first page offset in the range
 298  * @nr: Number of incremental page offsets to cover
 299  * @bitmap_pgoff: The page offset of the first bit in @bitmap
 300  * @bitmap: Pointer to a bitmap of at least @nr bits. The bitmap needs to
 301  * cover the whole range @first_index..@first_index + @nr.
 302  * @start: Pointer to number of the first set bit in @bitmap.
 303  * is modified as new bits are set by the function.
 304  * @end: Pointer to the number of the last set bit in @bitmap.
 305  * none set. The value is modified as new bits are set by the function.
 306  *
 307  * Note: When this function returns there is no guarantee that a CPU has
 308  * not already dirtied new ptes. However it will not clean any ptes not
 309  * reported in the bitmap. The guarantees are as follows:
 310  * a) All ptes dirty when the function starts executing will end up recorded
 311  *    in the bitmap.
 312  * b) All ptes dirtied after that will either remain dirty, be recorded in the
 313  *    bitmap or both.
 314  *
 315  * If a caller needs to make sure all dirty ptes are picked up and none
 316  * additional are added, it first needs to write-protect the address-space
 317  * range and make sure new writers are blocked in page_mkwrite() or
 318  * pfn_mkwrite(). And then after a TLB flush following the write-protection
 319  * pick up all dirty bits.
 320  *
 321  * This function currently skips transhuge page-table entries, since
 322  * it's intended for dirty-tracking on the PTE level. It will warn on
 323  * encountering transhuge dirty entries, though, and can easily be extended
 324  * to handle them as well.
 325  *
 326  * Return: The number of dirty ptes actually cleaned.
 327  */
 328 unsigned long clean_record_shared_mapping_range(struct address_space *mapping,
 329                                                 pgoff_t first_index, pgoff_t nr,
 330                                                 pgoff_t bitmap_pgoff,
 331                                                 unsigned long *bitmap,
 332                                                 pgoff_t *start,
 333                                                 pgoff_t *end)
 334 {
 335         bool none_set = (*start >= *end);
 336         struct clean_walk cwalk = {
 337                 .base = { .total = 0 },
 338                 .bitmap_pgoff = bitmap_pgoff,
 339                 .bitmap = bitmap,
 340                 .start = none_set ? nr : *start,
 341                 .end = none_set ? 0 : *end,
 342         };
 343
 344         i_mmap_lock_read(mapping);
 345         WARN_ON(walk_page_mapping(mapping, first_index, nr, &clean_walk_ops,
 346                                   &cwalk.base));
 347         i_mmap_unlock_read(mapping);
 348
 349         *start = cwalk.start;
 350         *end = cwalk.end;
 351
 352         return cwalk.base.total;
 353 }
 354 EXPORT_SYMBOL_GPL(clean_record_shared_mapping_range);