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 */
 17struct 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 */
 34static 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 */
 65struct 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 */
 89static 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 */
126static 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 */
156static 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 */
185static 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->vma, 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 */
214static 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 */
234static 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
247static 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
256static 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 */
279unsigned 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}
291EXPORT_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 */
328unsigned 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}
354EXPORT_SYMBOL_GPL(clean_record_shared_mapping_range);