page_vma_mapped.c

  1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/mm.h>
  3#include <linux/rmap.h>
  4#include <linux/hugetlb.h>
  5#include <linux/swap.h>
  6#include <linux/leafops.h>
  7
  8#include "internal.h"
  9
 10static inline bool not_found(struct page_vma_mapped_walk *pvmw)
 11{
 12	page_vma_mapped_walk_done(pvmw);
 13	return false;
 14}
 15
 16static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp,
 17		    spinlock_t **ptlp)
 18{
 19	bool is_migration;
 20	pte_t ptent;
 21
 22	if (pvmw->flags & PVMW_SYNC) {
 23		/* Use the stricter lookup */
 24		pvmw->pte = pte_offset_map_lock(pvmw->vma->vm_mm, pvmw->pmd,
 25						pvmw->address, &pvmw->ptl);
 26		*ptlp = pvmw->ptl;
 27		return !!pvmw->pte;
 28	}
 29
 30	is_migration = pvmw->flags & PVMW_MIGRATION;
 31again:
 32	/*
 33	 * It is important to return the ptl corresponding to pte,
 34	 * in case *pvmw->pmd changes underneath us; so we need to
 35	 * return it even when choosing not to lock, in case caller
 36	 * proceeds to loop over next ptes, and finds a match later.
 37	 * Though, in most cases, page lock already protects this.
 38	 */
 39	pvmw->pte = pte_offset_map_rw_nolock(pvmw->vma->vm_mm, pvmw->pmd,
 40					     pvmw->address, pmdvalp, ptlp);
 41	if (!pvmw->pte)
 42		return false;
 43
 44	ptent = ptep_get(pvmw->pte);
 45
 46	if (pte_none(ptent)) {
 47		return false;
 48	} else if (pte_present(ptent)) {
 49		if (is_migration)
 50			return false;
 51	} else if (!is_migration) {
 52		softleaf_t entry;
 53
 54		/*
 55		 * Handle un-addressable ZONE_DEVICE memory.
 56		 *
 57		 * We get here when we are trying to unmap a private
 58		 * device page from the process address space. Such
 59		 * page is not CPU accessible and thus is mapped as
 60		 * a special swap entry, nonetheless it still does
 61		 * count as a valid regular mapping for the page
 62		 * (and is accounted as such in page maps count).
 63		 *
 64		 * So handle this special case as if it was a normal
 65		 * page mapping ie lock CPU page table and return true.
 66		 *
 67		 * For more details on device private memory see HMM
 68		 * (include/linux/hmm.h or mm/hmm.c).
 69		 */
 70		entry = softleaf_from_pte(ptent);
 71		if (!softleaf_is_device_private(entry) &&
 72		    !softleaf_is_device_exclusive(entry))
 73			return false;
 74	}
 75	spin_lock(*ptlp);
 76	if (unlikely(!pmd_same(*pmdvalp, pmdp_get_lockless(pvmw->pmd)))) {
 77		pte_unmap_unlock(pvmw->pte, *ptlp);
 78		goto again;
 79	}
 80	pvmw->ptl = *ptlp;
 81
 82	return true;
 83}
 84
 85/**
 86 * check_pte - check if [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages) is
 87 * mapped at the @pvmw->pte
 88 * @pvmw: page_vma_mapped_walk struct, includes a pair pte and pfn range
 89 * for checking
 90 * @pte_nr: the number of small pages described by @pvmw->pte.
 91 *
 92 * page_vma_mapped_walk() found a place where pfn range is *potentially*
 93 * mapped. check_pte() has to validate this.
 94 *
 95 * pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
 96 * arbitrary page.
 97 *
 98 * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
 99 * entry that points to [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages)
100 *
101 * If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
102 * [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages)
103 *
104 * Otherwise, return false.
105 *
106 */
107static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
108{
109	unsigned long pfn;
110	pte_t ptent = ptep_get(pvmw->pte);
111
112	if (pvmw->flags & PVMW_MIGRATION) {
113		const softleaf_t entry = softleaf_from_pte(ptent);
114
115		if (!softleaf_is_migration(entry))
116			return false;
117
118		pfn = softleaf_to_pfn(entry);
119	} else if (pte_present(ptent)) {
120		pfn = pte_pfn(ptent);
121	} else {
122		const softleaf_t entry = softleaf_from_pte(ptent);
123
124		/* Handle un-addressable ZONE_DEVICE memory */
125		if (!softleaf_is_device_private(entry) &&
126		    !softleaf_is_device_exclusive(entry))
127			return false;
128
129		pfn = softleaf_to_pfn(entry);
130	}
131
132	if ((pfn + pte_nr - 1) < pvmw->pfn)
133		return false;
134	if (pfn > (pvmw->pfn + pvmw->nr_pages - 1))
135		return false;
136	return true;
137}
138
139/* Returns true if the two ranges overlap.  Careful to not overflow. */
140static bool check_pmd(unsigned long pfn, struct page_vma_mapped_walk *pvmw)
141{
142	if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn)
143		return false;
144	if (pfn > pvmw->pfn + pvmw->nr_pages - 1)
145		return false;
146	return true;
147}
148
149static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
150{
151	pvmw->address = (pvmw->address + size) & ~(size - 1);
152	if (!pvmw->address)
153		pvmw->address = ULONG_MAX;
154}
155
156/**
157 * page_vma_mapped_walk - check if @pvmw->pfn is mapped in @pvmw->vma at
158 * @pvmw->address
159 * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
160 * must be set. pmd, pte and ptl must be NULL.
161 *
162 * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
163 * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
164 * adjusted if needed (for PTE-mapped THPs).
165 *
166 * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
167 * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
168 * a loop to find all PTEs that map the THP.
169 *
170 * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
171 * regardless of which page table level the page is mapped at. @pvmw->pmd is
172 * NULL.
173 *
174 * Returns false if there are no more page table entries for the page in
175 * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
176 *
177 * If you need to stop the walk before page_vma_mapped_walk() returned false,
178 * use page_vma_mapped_walk_done(). It will do the housekeeping.
179 */
180bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
181{
182	struct vm_area_struct *vma = pvmw->vma;
183	struct mm_struct *mm = vma->vm_mm;
184	unsigned long end;
185	spinlock_t *ptl;
186	pgd_t *pgd;
187	p4d_t *p4d;
188	pud_t *pud;
189	pmd_t pmde;
190
191	/* The only possible pmd mapping has been handled on last iteration */
192	if (pvmw->pmd && !pvmw->pte)
193		return not_found(pvmw);
194
195	if (unlikely(is_vm_hugetlb_page(vma))) {
196		struct hstate *hstate = hstate_vma(vma);
197		unsigned long size = huge_page_size(hstate);
198		/* The only possible mapping was handled on last iteration */
199		if (pvmw->pte)
200			return not_found(pvmw);
201		/*
202		 * All callers that get here will already hold the
203		 * i_mmap_rwsem.  Therefore, no additional locks need to be
204		 * taken before calling hugetlb_walk().
205		 */
206		pvmw->pte = hugetlb_walk(vma, pvmw->address, size);
207		if (!pvmw->pte)
208			return false;
209
210		pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte);
211		if (!check_pte(pvmw, pages_per_huge_page(hstate)))
212			return not_found(pvmw);
213		return true;
214	}
215
216	end = vma_address_end(pvmw);
217	if (pvmw->pte)
218		goto next_pte;
219restart:
220	do {
221		pgd = pgd_offset(mm, pvmw->address);
222		if (!pgd_present(*pgd)) {
223			step_forward(pvmw, PGDIR_SIZE);
224			continue;
225		}
226		p4d = p4d_offset(pgd, pvmw->address);
227		if (!p4d_present(*p4d)) {
228			step_forward(pvmw, P4D_SIZE);
229			continue;
230		}
231		pud = pud_offset(p4d, pvmw->address);
232		if (!pud_present(*pud)) {
233			step_forward(pvmw, PUD_SIZE);
234			continue;
235		}
236
237		pvmw->pmd = pmd_offset(pud, pvmw->address);
238		/*
239		 * Make sure the pmd value isn't cached in a register by the
240		 * compiler and used as a stale value after we've observed a
241		 * subsequent update.
242		 */
243		pmde = pmdp_get_lockless(pvmw->pmd);
244
245		if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde)) {
246			pvmw->ptl = pmd_lock(mm, pvmw->pmd);
247			pmde = *pvmw->pmd;
248			if (!pmd_present(pmde)) {
249				softleaf_t entry;
250
251				if (!thp_migration_supported() ||
252				    !(pvmw->flags & PVMW_MIGRATION))
253					return not_found(pvmw);
254				entry = softleaf_from_pmd(pmde);
255
256				if (!softleaf_is_migration(entry) ||
257				    !check_pmd(softleaf_to_pfn(entry), pvmw))
258					return not_found(pvmw);
259				return true;
260			}
261			if (likely(pmd_trans_huge(pmde))) {
262				if (pvmw->flags & PVMW_MIGRATION)
263					return not_found(pvmw);
264				if (!check_pmd(pmd_pfn(pmde), pvmw))
265					return not_found(pvmw);
266				return true;
267			}
268			/* THP pmd was split under us: handle on pte level */
269			spin_unlock(pvmw->ptl);
270			pvmw->ptl = NULL;
271		} else if (!pmd_present(pmde)) {
272			/*
273			 * If PVMW_SYNC, take and drop THP pmd lock so that we
274			 * cannot return prematurely, while zap_huge_pmd() has
275			 * cleared *pmd but not decremented compound_mapcount().
276			 */
277			const softleaf_t entry = softleaf_from_pmd(pmde);
278
279			if (softleaf_is_device_private(entry)) {
280				pvmw->ptl = pmd_lock(mm, pvmw->pmd);
281				return true;
282			}
283
284			if ((pvmw->flags & PVMW_SYNC) &&
285			    thp_vma_suitable_order(vma, pvmw->address,
286						   PMD_ORDER) &&
287			    (pvmw->nr_pages >= HPAGE_PMD_NR)) {
288				spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
289
290				spin_unlock(ptl);
291			}
292			step_forward(pvmw, PMD_SIZE);
293			continue;
294		}
295		if (!map_pte(pvmw, &pmde, &ptl)) {
296			if (!pvmw->pte)
297				goto restart;
298			goto next_pte;
299		}
300this_pte:
301		if (check_pte(pvmw, 1))
302			return true;
303next_pte:
304		do {
305			pvmw->address += PAGE_SIZE;
306			if (pvmw->address >= end)
307				return not_found(pvmw);
308			/* Did we cross page table boundary? */
309			if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
310				if (pvmw->ptl) {
311					spin_unlock(pvmw->ptl);
312					pvmw->ptl = NULL;
313				}
314				pte_unmap(pvmw->pte);
315				pvmw->pte = NULL;
316				pvmw->flags |= PVMW_PGTABLE_CROSSED;
317				goto restart;
318			}
319			pvmw->pte++;
320		} while (pte_none(ptep_get(pvmw->pte)));
321
322		if (!pvmw->ptl) {
323			spin_lock(ptl);
324			if (unlikely(!pmd_same(pmde, pmdp_get_lockless(pvmw->pmd)))) {
325				pte_unmap_unlock(pvmw->pte, ptl);
326				pvmw->pte = NULL;
327				goto restart;
328			}
329			pvmw->ptl = ptl;
330		}
331		goto this_pte;
332	} while (pvmw->address < end);
333
334	return false;
335}
336
337#ifdef CONFIG_MEMORY_FAILURE
338/**
339 * page_mapped_in_vma - check whether a page is really mapped in a VMA
340 * @page: the page to test
341 * @vma: the VMA to test
342 *
343 * Return: The address the page is mapped at if the page is in the range
344 * covered by the VMA and present in the page table.  If the page is
345 * outside the VMA or not present, returns -EFAULT.
346 * Only valid for normal file or anonymous VMAs.
347 */
348unsigned long page_mapped_in_vma(const struct page *page,
349		struct vm_area_struct *vma)
350{
351	const struct folio *folio = page_folio(page);
352	struct page_vma_mapped_walk pvmw = {
353		.pfn = page_to_pfn(page),
354		.nr_pages = 1,
355		.vma = vma,
356		.flags = PVMW_SYNC,
357	};
358
359	pvmw.address = vma_address(vma, page_pgoff(folio, page), 1);
360	if (pvmw.address == -EFAULT)
361		goto out;
362	if (!page_vma_mapped_walk(&pvmw))
363		return -EFAULT;
364	page_vma_mapped_walk_done(&pvmw);
365out:
366	return pvmw.address;
367}
368#endif