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 = ptep_get(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 = ptep_get(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         /* Do not split a huge pmd, present or migrated */
 132         if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval)) {
 133                 WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));
 134                 walk->action = ACTION_CONTINUE;
 135         }
 136         return 0;
 137 }
 138
 139 /*
 140  * wp_clean_pud_entry - The pagewalk pud callback.
 141  *
 142  * Dirty-tracking should take place on the PTE level, so
 143  * WARN() if encountering a dirty huge puds.
 144  * Furthermore, never split huge puds, since that currently
 145  * causes dirty info loss. The pagefault handler should do
 146  * that if needed.
 147  */
 148 static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
 149                               struct mm_walk *walk)
 150 {
 151 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 152         pud_t pudval = READ_ONCE(*pud);
 153
 154         /* Do not split a huge pud */
 155         if (pud_trans_huge(pudval) || pud_devmap(pudval)) {
 156                 WARN_ON(pud_write(pudval) || pud_dirty(pudval));
 157                 walk->action = ACTION_CONTINUE;
 158         }
 159 #endif
 160         return 0;
 161 }
 162
 163 /*
 164  * wp_clean_pre_vma - The pagewalk pre_vma callback.
 165  *
 166  * The pre_vma callback performs the cache flush, stages the tlb flush
 167  * and calls the necessary mmu notifiers.
 168  */
 169 static int wp_clean_pre_vma(unsigned long start, unsigned long end,
 170                             struct mm_walk *walk)
 171 {
 172         struct wp_walk *wpwalk = walk->private;
 173
 174         wpwalk->tlbflush_start = end;
 175         wpwalk->tlbflush_end = start;
 176
 177         mmu_notifier_range_init(&wpwalk->range, MMU_NOTIFY_PROTECTION_PAGE, 0,
 178                                 walk->mm, start, end);
 179         mmu_notifier_invalidate_range_start(&wpwalk->range);
 180         flush_cache_range(walk->vma, start, end);
 181
 182         /*
 183          * We're not using tlb_gather_mmu() since typically
 184          * only a small subrange of PTEs are affected, whereas
 185          * tlb_gather_mmu() records the full range.
 186          */
 187         inc_tlb_flush_pending(walk->mm);
 188
 189         return 0;
 190 }
 191
 192 /*
 193  * wp_clean_post_vma - The pagewalk post_vma callback.
 194  *
 195  * The post_vma callback performs the tlb flush and calls necessary mmu
 196  * notifiers.
 197  */
 198 static void wp_clean_post_vma(struct mm_walk *walk)
 199 {
 200         struct wp_walk *wpwalk = walk->private;
 201
 202         if (mm_tlb_flush_nested(walk->mm))
 203                 flush_tlb_range(walk->vma, wpwalk->range.start,
 204                                 wpwalk->range.end);
 205         else if (wpwalk->tlbflush_end > wpwalk->tlbflush_start)
 206                 flush_tlb_range(walk->vma, wpwalk->tlbflush_start,
 207                                 wpwalk->tlbflush_end);
 208
 209         mmu_notifier_invalidate_range_end(&wpwalk->range);
 210         dec_tlb_flush_pending(walk->mm);
 211 }
 212
 213 /*
 214  * wp_clean_test_walk - The pagewalk test_walk callback.
 215  *
 216  * Won't perform dirty-tracking on COW, read-only or HUGETLB vmas.
 217  */
 218 static int wp_clean_test_walk(unsigned long start, unsigned long end,
 219                               struct mm_walk *walk)
 220 {
 221         unsigned long vm_flags = READ_ONCE(walk->vma->vm_flags);
 222
 223         /* Skip non-applicable VMAs */
 224         if ((vm_flags & (VM_SHARED | VM_MAYWRITE | VM_HUGETLB)) !=
 225             (VM_SHARED | VM_MAYWRITE))
 226                 return 1;
 227
 228         return 0;
 229 }
 230
 231 static const struct mm_walk_ops clean_walk_ops = {
 232         .pte_entry = clean_record_pte,
 233         .pmd_entry = wp_clean_pmd_entry,
 234         .pud_entry = wp_clean_pud_entry,
 235         .test_walk = wp_clean_test_walk,
 236         .pre_vma = wp_clean_pre_vma,
 237         .post_vma = wp_clean_post_vma
 238 };
 239
 240 static const struct mm_walk_ops wp_walk_ops = {
 241         .pte_entry = wp_pte,
 242         .pmd_entry = wp_clean_pmd_entry,
 243         .pud_entry = wp_clean_pud_entry,
 244         .test_walk = wp_clean_test_walk,
 245         .pre_vma = wp_clean_pre_vma,
 246         .post_vma = wp_clean_post_vma
 247 };
 248
 249 /**
 250  * wp_shared_mapping_range - Write-protect all ptes in an address space range
 251  * @mapping: The address_space we want to write protect
 252  * @first_index: The first page offset in the range
 253  * @nr: Number of incremental page offsets to cover
 254  *
 255  * Note: This function currently skips transhuge page-table entries, since
 256  * it's intended for dirty-tracking on the PTE level. It will warn on
 257  * encountering transhuge write-enabled entries, though, and can easily be
 258  * extended to handle them as well.
 259  *
 260  * Return: The number of ptes actually write-protected. Note that
 261  * already write-protected ptes are not counted.
 262  */
 263 unsigned long wp_shared_mapping_range(struct address_space *mapping,
 264                                       pgoff_t first_index, pgoff_t nr)
 265 {
 266         struct wp_walk wpwalk = { .total = 0 };
 267
 268         i_mmap_lock_read(mapping);
 269         WARN_ON(walk_page_mapping(mapping, first_index, nr, &wp_walk_ops,
 270                                   &wpwalk));
 271         i_mmap_unlock_read(mapping);
 272
 273         return wpwalk.total;
 274 }
 275 EXPORT_SYMBOL_GPL(wp_shared_mapping_range);
 276
 277 /**
 278  * clean_record_shared_mapping_range - Clean and record all ptes in an
 279  * address space range
 280  * @mapping: The address_space we want to clean
 281  * @first_index: The first page offset in the range
 282  * @nr: Number of incremental page offsets to cover
 283  * @bitmap_pgoff: The page offset of the first bit in @bitmap
 284  * @bitmap: Pointer to a bitmap of at least @nr bits. The bitmap needs to
 285  * cover the whole range @first_index..@first_index + @nr.
 286  * @start: Pointer to number of the first set bit in @bitmap.
 287  * is modified as new bits are set by the function.
 288  * @end: Pointer to the number of the last set bit in @bitmap.
 289  * none set. The value is modified as new bits are set by the function.
 290  *
 291  * When this function returns there is no guarantee that a CPU has
 292  * not already dirtied new ptes. However it will not clean any ptes not
 293  * reported in the bitmap. The guarantees are as follows:
 294  *
 295  * * All ptes dirty when the function starts executing will end up recorded
 296  *   in the bitmap.
 297  * * All ptes dirtied after that will either remain dirty, be recorded in the
 298  *   bitmap or both.
 299  *
 300  * If a caller needs to make sure all dirty ptes are picked up and none
 301  * additional are added, it first needs to write-protect the address-space
 302  * range and make sure new writers are blocked in page_mkwrite() or
 303  * pfn_mkwrite(). And then after a TLB flush following the write-protection
 304  * pick up all dirty bits.
 305  *
 306  * This function currently skips transhuge page-table entries, since
 307  * it's intended for dirty-tracking on the PTE level. It will warn on
 308  * encountering transhuge dirty entries, though, and can easily be extended
 309  * to handle them as well.
 310  *
 311  * Return: The number of dirty ptes actually cleaned.
 312  */
 313 unsigned long clean_record_shared_mapping_range(struct address_space *mapping,
 314                                                 pgoff_t first_index, pgoff_t nr,
 315                                                 pgoff_t bitmap_pgoff,
 316                                                 unsigned long *bitmap,
 317                                                 pgoff_t *start,
 318                                                 pgoff_t *end)
 319 {
 320         bool none_set = (*start >= *end);
 321         struct clean_walk cwalk = {
 322                 .base = { .total = 0 },
 323                 .bitmap_pgoff = bitmap_pgoff,
 324                 .bitmap = bitmap,
 325                 .start = none_set ? nr : *start,
 326                 .end = none_set ? 0 : *end,
 327         };
 328
 329         i_mmap_lock_read(mapping);
 330         WARN_ON(walk_page_mapping(mapping, first_index, nr, &clean_walk_ops,
 331                                   &cwalk.base));
 332         i_mmap_unlock_read(mapping);
 333
 334         *start = cwalk.start;
 335         *end = cwalk.end;
 336
 337         return cwalk.base.total;
 338 }
 339 EXPORT_SYMBOL_GPL(clean_record_shared_mapping_range);