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