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