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 = *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 = *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 if (!pmd_trans_unstable(&pmdval)) 132 return 0; 133 134 if (pmd_none(pmdval)) { 135 walk->action = ACTION_AGAIN; 136 return 0; 137 } 138 139 /* Huge pmd, present or migrated */ 140 walk->action = ACTION_CONTINUE; 141 if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval)) 142 WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval)); 143 144 return 0; 145 } 146 147 /* 148 * wp_clean_pud_entry - The pagewalk pud callback. 149 * 150 * Dirty-tracking should take place on the PTE level, so 151 * WARN() if encountering a dirty huge puds. 152 * Furthermore, never split huge puds, since that currently 153 * causes dirty info loss. The pagefault handler should do 154 * that if needed. 155 */ 156 static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end, 157 struct mm_walk *walk) 158 { 159 pud_t pudval = READ_ONCE(*pud); 160 161 if (!pud_trans_unstable(&pudval)) 162 return 0; 163 164 if (pud_none(pudval)) { 165 walk->action = ACTION_AGAIN; 166 return 0; 167 } 168 169 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD 170 /* Huge pud */ 171 walk->action = ACTION_CONTINUE; 172 if (pud_trans_huge(pudval) || pud_devmap(pudval)) 173 WARN_ON(pud_write(pudval) || pud_dirty(pudval)); 174 #endif 175 176 return 0; 177 } 178 179 /* 180 * wp_clean_pre_vma - The pagewalk pre_vma callback. 181 * 182 * The pre_vma callback performs the cache flush, stages the tlb flush 183 * and calls the necessary mmu notifiers. 184 */ 185 static int wp_clean_pre_vma(unsigned long start, unsigned long end, 186 struct mm_walk *walk) 187 { 188 struct wp_walk *wpwalk = walk->private; 189 190 wpwalk->tlbflush_start = end; 191 wpwalk->tlbflush_end = start; 192 193 mmu_notifier_range_init(&wpwalk->range, MMU_NOTIFY_PROTECTION_PAGE, 0, 194 walk->mm, start, end); 195 mmu_notifier_invalidate_range_start(&wpwalk->range); 196 flush_cache_range(walk->vma, start, end); 197 198 /* 199 * We're not using tlb_gather_mmu() since typically 200 * only a small subrange of PTEs are affected, whereas 201 * tlb_gather_mmu() records the full range. 202 */ 203 inc_tlb_flush_pending(walk->mm); 204 205 return 0; 206 } 207 208 /* 209 * wp_clean_post_vma - The pagewalk post_vma callback. 210 * 211 * The post_vma callback performs the tlb flush and calls necessary mmu 212 * notifiers. 213 */ 214 static void wp_clean_post_vma(struct mm_walk *walk) 215 { 216 struct wp_walk *wpwalk = walk->private; 217 218 if (mm_tlb_flush_nested(walk->mm)) 219 flush_tlb_range(walk->vma, wpwalk->range.start, 220 wpwalk->range.end); 221 else if (wpwalk->tlbflush_end > wpwalk->tlbflush_start) 222 flush_tlb_range(walk->vma, wpwalk->tlbflush_start, 223 wpwalk->tlbflush_end); 224 225 mmu_notifier_invalidate_range_end(&wpwalk->range); 226 dec_tlb_flush_pending(walk->mm); 227 } 228 229 /* 230 * wp_clean_test_walk - The pagewalk test_walk callback. 231 * 232 * Won't perform dirty-tracking on COW, read-only or HUGETLB vmas. 233 */ 234 static int wp_clean_test_walk(unsigned long start, unsigned long end, 235 struct mm_walk *walk) 236 { 237 unsigned long vm_flags = READ_ONCE(walk->vma->vm_flags); 238 239 /* Skip non-applicable VMAs */ 240 if ((vm_flags & (VM_SHARED | VM_MAYWRITE | VM_HUGETLB)) != 241 (VM_SHARED | VM_MAYWRITE)) 242 return 1; 243 244 return 0; 245 } 246 247 static const struct mm_walk_ops clean_walk_ops = { 248 .pte_entry = clean_record_pte, 249 .pmd_entry = wp_clean_pmd_entry, 250 .pud_entry = wp_clean_pud_entry, 251 .test_walk = wp_clean_test_walk, 252 .pre_vma = wp_clean_pre_vma, 253 .post_vma = wp_clean_post_vma 254 }; 255 256 static const struct mm_walk_ops wp_walk_ops = { 257 .pte_entry = wp_pte, 258 .pmd_entry = wp_clean_pmd_entry, 259 .pud_entry = wp_clean_pud_entry, 260 .test_walk = wp_clean_test_walk, 261 .pre_vma = wp_clean_pre_vma, 262 .post_vma = wp_clean_post_vma 263 }; 264 265 /** 266 * wp_shared_mapping_range - Write-protect all ptes in an address space range 267 * @mapping: The address_space we want to write protect 268 * @first_index: The first page offset in the range 269 * @nr: Number of incremental page offsets to cover 270 * 271 * Note: This function currently skips transhuge page-table entries, since 272 * it's intended for dirty-tracking on the PTE level. It will warn on 273 * encountering transhuge write-enabled entries, though, and can easily be 274 * extended to handle them as well. 275 * 276 * Return: The number of ptes actually write-protected. Note that 277 * already write-protected ptes are not counted. 278 */ 279 unsigned long wp_shared_mapping_range(struct address_space *mapping, 280 pgoff_t first_index, pgoff_t nr) 281 { 282 struct wp_walk wpwalk = { .total = 0 }; 283 284 i_mmap_lock_read(mapping); 285 WARN_ON(walk_page_mapping(mapping, first_index, nr, &wp_walk_ops, 286 &wpwalk)); 287 i_mmap_unlock_read(mapping); 288 289 return wpwalk.total; 290 } 291 EXPORT_SYMBOL_GPL(wp_shared_mapping_range); 292 293 /** 294 * clean_record_shared_mapping_range - Clean and record all ptes in an 295 * address space range 296 * @mapping: The address_space we want to clean 297 * @first_index: The first page offset in the range 298 * @nr: Number of incremental page offsets to cover 299 * @bitmap_pgoff: The page offset of the first bit in @bitmap 300 * @bitmap: Pointer to a bitmap of at least @nr bits. The bitmap needs to 301 * cover the whole range @first_index..@first_index + @nr. 302 * @start: Pointer to number of the first set bit in @bitmap. 303 * is modified as new bits are set by the function. 304 * @end: Pointer to the number of the last set bit in @bitmap. 305 * none set. The value is modified as new bits are set by the function. 306 * 307 * Note: When this function returns there is no guarantee that a CPU has 308 * not already dirtied new ptes. However it will not clean any ptes not 309 * reported in the bitmap. The guarantees are as follows: 310 * a) All ptes dirty when the function starts executing will end up recorded 311 * in the bitmap. 312 * b) All ptes dirtied after that will either remain dirty, be recorded in the 313 * bitmap or both. 314 * 315 * If a caller needs to make sure all dirty ptes are picked up and none 316 * additional are added, it first needs to write-protect the address-space 317 * range and make sure new writers are blocked in page_mkwrite() or 318 * pfn_mkwrite(). And then after a TLB flush following the write-protection 319 * pick up all dirty bits. 320 * 321 * This function currently skips transhuge page-table entries, since 322 * it's intended for dirty-tracking on the PTE level. It will warn on 323 * encountering transhuge dirty entries, though, and can easily be extended 324 * to handle them as well. 325 * 326 * Return: The number of dirty ptes actually cleaned. 327 */ 328 unsigned long clean_record_shared_mapping_range(struct address_space *mapping, 329 pgoff_t first_index, pgoff_t nr, 330 pgoff_t bitmap_pgoff, 331 unsigned long *bitmap, 332 pgoff_t *start, 333 pgoff_t *end) 334 { 335 bool none_set = (*start >= *end); 336 struct clean_walk cwalk = { 337 .base = { .total = 0 }, 338 .bitmap_pgoff = bitmap_pgoff, 339 .bitmap = bitmap, 340 .start = none_set ? nr : *start, 341 .end = none_set ? 0 : *end, 342 }; 343 344 i_mmap_lock_read(mapping); 345 WARN_ON(walk_page_mapping(mapping, first_index, nr, &clean_walk_ops, 346 &cwalk.base)); 347 i_mmap_unlock_read(mapping); 348 349 *start = cwalk.start; 350 *end = cwalk.end; 351 352 return cwalk.base.total; 353 } 354 EXPORT_SYMBOL_GPL(clean_record_shared_mapping_range); 355