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