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 /* wp_clean_pmd_entry - The pagewalk pmd callback. */
 115 static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
 116                               struct mm_walk *walk)
 117 {
 118         /* Dirty-tracking should be handled on the pte level */
 119         pmd_t pmdval = pmd_read_atomic(pmd);
 120
 121         if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
 122                 WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));
 123
 124         return 0;
 125 }
 126
 127 /* wp_clean_pud_entry - The pagewalk pud callback. */
 128 static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
 129                               struct mm_walk *walk)
 130 {
 131         /* Dirty-tracking should be handled on the pte level */
 132         pud_t pudval = READ_ONCE(*pud);
 133
 134         if (pud_trans_huge(pudval) || pud_devmap(pudval))
 135                 WARN_ON(pud_write(pudval) || pud_dirty(pudval));
 136
 137         return 0;
 138 }
 139
 140 /*
 141  * wp_clean_pre_vma - The pagewalk pre_vma callback.
 142  *
 143  * The pre_vma callback performs the cache flush, stages the tlb flush
 144  * and calls the necessary mmu notifiers.
 145  */
 146 static int wp_clean_pre_vma(unsigned long start, unsigned long end,
 147                             struct mm_walk *walk)
 148 {
 149         struct wp_walk *wpwalk = walk->private;
 150
 151         wpwalk->tlbflush_start = end;
 152         wpwalk->tlbflush_end = start;
 153
 154         mmu_notifier_range_init(&wpwalk->range, MMU_NOTIFY_PROTECTION_PAGE, 0,
 155                                 walk->vma, walk->mm, start, end);
 156         mmu_notifier_invalidate_range_start(&wpwalk->range);
 157         flush_cache_range(walk->vma, start, end);
 158
 159         /*
 160          * We're not using tlb_gather_mmu() since typically
 161          * only a small subrange of PTEs are affected, whereas
 162          * tlb_gather_mmu() records the full range.
 163          */
 164         inc_tlb_flush_pending(walk->mm);
 165
 166         return 0;
 167 }
 168
 169 /*
 170  * wp_clean_post_vma - The pagewalk post_vma callback.
 171  *
 172  * The post_vma callback performs the tlb flush and calls necessary mmu
 173  * notifiers.
 174  */
 175 static void wp_clean_post_vma(struct mm_walk *walk)
 176 {
 177         struct wp_walk *wpwalk = walk->private;
 178
 179         if (mm_tlb_flush_nested(walk->mm))
 180                 flush_tlb_range(walk->vma, wpwalk->range.start,
 181                                 wpwalk->range.end);
 182         else if (wpwalk->tlbflush_end > wpwalk->tlbflush_start)
 183                 flush_tlb_range(walk->vma, wpwalk->tlbflush_start,
 184                                 wpwalk->tlbflush_end);
 185
 186         mmu_notifier_invalidate_range_end(&wpwalk->range);
 187         dec_tlb_flush_pending(walk->mm);
 188 }
 189
 190 /*
 191  * wp_clean_test_walk - The pagewalk test_walk callback.
 192  *
 193  * Won't perform dirty-tracking on COW, read-only or HUGETLB vmas.
 194  */
 195 static int wp_clean_test_walk(unsigned long start, unsigned long end,
 196                               struct mm_walk *walk)
 197 {
 198         unsigned long vm_flags = READ_ONCE(walk->vma->vm_flags);
 199
 200         /* Skip non-applicable VMAs */
 201         if ((vm_flags & (VM_SHARED | VM_MAYWRITE | VM_HUGETLB)) !=
 202             (VM_SHARED | VM_MAYWRITE))
 203                 return 1;
 204
 205         return 0;
 206 }
 207
 208 static const struct mm_walk_ops clean_walk_ops = {
 209         .pte_entry = clean_record_pte,
 210         .pmd_entry = wp_clean_pmd_entry,
 211         .pud_entry = wp_clean_pud_entry,
 212         .test_walk = wp_clean_test_walk,
 213         .pre_vma = wp_clean_pre_vma,
 214         .post_vma = wp_clean_post_vma
 215 };
 216
 217 static const struct mm_walk_ops wp_walk_ops = {
 218         .pte_entry = wp_pte,
 219         .pmd_entry = wp_clean_pmd_entry,
 220         .pud_entry = wp_clean_pud_entry,
 221         .test_walk = wp_clean_test_walk,
 222         .pre_vma = wp_clean_pre_vma,
 223         .post_vma = wp_clean_post_vma
 224 };
 225
 226 /**
 227  * wp_shared_mapping_range - Write-protect all ptes in an address space range
 228  * @mapping: The address_space we want to write protect
 229  * @first_index: The first page offset in the range
 230  * @nr: Number of incremental page offsets to cover
 231  *
 232  * Note: This function currently skips transhuge page-table entries, since
 233  * it's intended for dirty-tracking on the PTE level. It will warn on
 234  * encountering transhuge write-enabled entries, though, and can easily be
 235  * extended to handle them as well.
 236  *
 237  * Return: The number of ptes actually write-protected. Note that
 238  * already write-protected ptes are not counted.
 239  */
 240 unsigned long wp_shared_mapping_range(struct address_space *mapping,
 241                                       pgoff_t first_index, pgoff_t nr)
 242 {
 243         struct wp_walk wpwalk = { .total = 0 };
 244
 245         i_mmap_lock_read(mapping);
 246         WARN_ON(walk_page_mapping(mapping, first_index, nr, &wp_walk_ops,
 247                                   &wpwalk));
 248         i_mmap_unlock_read(mapping);
 249
 250         return wpwalk.total;
 251 }
 252 EXPORT_SYMBOL_GPL(wp_shared_mapping_range);
 253
 254 /**
 255  * clean_record_shared_mapping_range - Clean and record all ptes in an
 256  * address space range
 257  * @mapping: The address_space we want to clean
 258  * @first_index: The first page offset in the range
 259  * @nr: Number of incremental page offsets to cover
 260  * @bitmap_pgoff: The page offset of the first bit in @bitmap
 261  * @bitmap: Pointer to a bitmap of at least @nr bits. The bitmap needs to
 262  * cover the whole range @first_index..@first_index + @nr.
 263  * @start: Pointer to number of the first set bit in @bitmap.
 264  * is modified as new bits are set by the function.
 265  * @end: Pointer to the number of the last set bit in @bitmap.
 266  * none set. The value is modified as new bits are set by the function.
 267  *
 268  * Note: When this function returns there is no guarantee that a CPU has
 269  * not already dirtied new ptes. However it will not clean any ptes not
 270  * reported in the bitmap. The guarantees are as follows:
 271  * a) All ptes dirty when the function starts executing will end up recorded
 272  *    in the bitmap.
 273  * b) All ptes dirtied after that will either remain dirty, be recorded in the
 274  *    bitmap or both.
 275  *
 276  * If a caller needs to make sure all dirty ptes are picked up and none
 277  * additional are added, it first needs to write-protect the address-space
 278  * range and make sure new writers are blocked in page_mkwrite() or
 279  * pfn_mkwrite(). And then after a TLB flush following the write-protection
 280  * pick up all dirty bits.
 281  *
 282  * Note: This function currently skips transhuge page-table entries, since
 283  * it's intended for dirty-tracking on the PTE level. It will warn on
 284  * encountering transhuge dirty entries, though, and can easily be extended
 285  * to handle them as well.
 286  *
 287  * Return: The number of dirty ptes actually cleaned.
 288  */
 289 unsigned long clean_record_shared_mapping_range(struct address_space *mapping,
 290                                                 pgoff_t first_index, pgoff_t nr,
 291                                                 pgoff_t bitmap_pgoff,
 292                                                 unsigned long *bitmap,
 293                                                 pgoff_t *start,
 294                                                 pgoff_t *end)
 295 {
 296         bool none_set = (*start >= *end);
 297         struct clean_walk cwalk = {
 298                 .base = { .total = 0 },
 299                 .bitmap_pgoff = bitmap_pgoff,
 300                 .bitmap = bitmap,
 301                 .start = none_set ? nr : *start,
 302                 .end = none_set ? 0 : *end,
 303         };
 304
 305         i_mmap_lock_read(mapping);
 306         WARN_ON(walk_page_mapping(mapping, first_index, nr, &clean_walk_ops,
 307                                   &cwalk.base));
 308         i_mmap_unlock_read(mapping);
 309
 310         *start = cwalk.start;
 311         *end = cwalk.end;
 312
 313         return cwalk.base.total;
 314 }
 315 EXPORT_SYMBOL_GPL(clean_record_shared_mapping_range);