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); 350