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 */
wp_pte(pte_t * pte,unsigned long addr,unsigned long end,struct mm_walk * walk)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 */
clean_record_pte(pte_t * pte,unsigned long addr,unsigned long end,struct mm_walk * walk)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 */
wp_clean_pmd_entry(pmd_t * pmd,unsigned long addr,unsigned long end,struct mm_walk * walk)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 */
wp_clean_pud_entry(pud_t * pud,unsigned long addr,unsigned long end,struct mm_walk * walk)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 */
wp_clean_pre_vma(unsigned long start,unsigned long end,struct mm_walk * walk)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 */
wp_clean_post_vma(struct mm_walk * walk)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 */
wp_clean_test_walk(unsigned long start,unsigned long end,struct mm_walk * walk)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 */
wp_shared_mapping_range(struct address_space * mapping,pgoff_t first_index,pgoff_t nr)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 */
clean_record_shared_mapping_range(struct address_space * mapping,pgoff_t first_index,pgoff_t nr,pgoff_t bitmap_pgoff,unsigned long * bitmap,pgoff_t * start,pgoff_t * end)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