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