xref: /linux/mm/page_vma_mapped.c (revision c33c7948)
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 
10 static inline bool not_found(struct page_vma_mapped_walk *pvmw)
11 {
12 	page_vma_mapped_walk_done(pvmw);
13 	return false;
14 }
15 
16 static 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->page is mapped at the @pvmw->pte
77  * @pvmw: page_vma_mapped_walk struct, includes a pair pte and page for checking
78  *
79  * page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
80  * mapped. check_pte() has to validate this.
81  *
82  * pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
83  * arbitrary page.
84  *
85  * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
86  * entry that points to @pvmw->page or any subpage in case of THP.
87  *
88  * If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
89  * pvmw->page or any subpage in case of THP.
90  *
91  * Otherwise, return false.
92  *
93  */
94 static bool check_pte(struct page_vma_mapped_walk *pvmw)
95 {
96 	unsigned long pfn;
97 	pte_t ptent = ptep_get(pvmw->pte);
98 
99 	if (pvmw->flags & PVMW_MIGRATION) {
100 		swp_entry_t entry;
101 		if (!is_swap_pte(ptent))
102 			return false;
103 		entry = pte_to_swp_entry(ptent);
104 
105 		if (!is_migration_entry(entry) &&
106 		    !is_device_exclusive_entry(entry))
107 			return false;
108 
109 		pfn = swp_offset_pfn(entry);
110 	} else if (is_swap_pte(ptent)) {
111 		swp_entry_t entry;
112 
113 		/* Handle un-addressable ZONE_DEVICE memory */
114 		entry = pte_to_swp_entry(ptent);
115 		if (!is_device_private_entry(entry) &&
116 		    !is_device_exclusive_entry(entry))
117 			return false;
118 
119 		pfn = swp_offset_pfn(entry);
120 	} else {
121 		if (!pte_present(ptent))
122 			return false;
123 
124 		pfn = pte_pfn(ptent);
125 	}
126 
127 	return (pfn - pvmw->pfn) < pvmw->nr_pages;
128 }
129 
130 /* Returns true if the two ranges overlap.  Careful to not overflow. */
131 static bool check_pmd(unsigned long pfn, struct page_vma_mapped_walk *pvmw)
132 {
133 	if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn)
134 		return false;
135 	if (pfn > pvmw->pfn + pvmw->nr_pages - 1)
136 		return false;
137 	return true;
138 }
139 
140 static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
141 {
142 	pvmw->address = (pvmw->address + size) & ~(size - 1);
143 	if (!pvmw->address)
144 		pvmw->address = ULONG_MAX;
145 }
146 
147 /**
148  * page_vma_mapped_walk - check if @pvmw->pfn is mapped in @pvmw->vma at
149  * @pvmw->address
150  * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
151  * must be set. pmd, pte and ptl must be NULL.
152  *
153  * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
154  * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
155  * adjusted if needed (for PTE-mapped THPs).
156  *
157  * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
158  * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
159  * a loop to find all PTEs that map the THP.
160  *
161  * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
162  * regardless of which page table level the page is mapped at. @pvmw->pmd is
163  * NULL.
164  *
165  * Returns false if there are no more page table entries for the page in
166  * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
167  *
168  * If you need to stop the walk before page_vma_mapped_walk() returned false,
169  * use page_vma_mapped_walk_done(). It will do the housekeeping.
170  */
171 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
172 {
173 	struct vm_area_struct *vma = pvmw->vma;
174 	struct mm_struct *mm = vma->vm_mm;
175 	unsigned long end;
176 	spinlock_t *ptl;
177 	pgd_t *pgd;
178 	p4d_t *p4d;
179 	pud_t *pud;
180 	pmd_t pmde;
181 
182 	/* The only possible pmd mapping has been handled on last iteration */
183 	if (pvmw->pmd && !pvmw->pte)
184 		return not_found(pvmw);
185 
186 	if (unlikely(is_vm_hugetlb_page(vma))) {
187 		struct hstate *hstate = hstate_vma(vma);
188 		unsigned long size = huge_page_size(hstate);
189 		/* The only possible mapping was handled on last iteration */
190 		if (pvmw->pte)
191 			return not_found(pvmw);
192 		/*
193 		 * All callers that get here will already hold the
194 		 * i_mmap_rwsem.  Therefore, no additional locks need to be
195 		 * taken before calling hugetlb_walk().
196 		 */
197 		pvmw->pte = hugetlb_walk(vma, pvmw->address, size);
198 		if (!pvmw->pte)
199 			return false;
200 
201 		pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte);
202 		if (!check_pte(pvmw))
203 			return not_found(pvmw);
204 		return true;
205 	}
206 
207 	end = vma_address_end(pvmw);
208 	if (pvmw->pte)
209 		goto next_pte;
210 restart:
211 	do {
212 		pgd = pgd_offset(mm, pvmw->address);
213 		if (!pgd_present(*pgd)) {
214 			step_forward(pvmw, PGDIR_SIZE);
215 			continue;
216 		}
217 		p4d = p4d_offset(pgd, pvmw->address);
218 		if (!p4d_present(*p4d)) {
219 			step_forward(pvmw, P4D_SIZE);
220 			continue;
221 		}
222 		pud = pud_offset(p4d, pvmw->address);
223 		if (!pud_present(*pud)) {
224 			step_forward(pvmw, PUD_SIZE);
225 			continue;
226 		}
227 
228 		pvmw->pmd = pmd_offset(pud, pvmw->address);
229 		/*
230 		 * Make sure the pmd value isn't cached in a register by the
231 		 * compiler and used as a stale value after we've observed a
232 		 * subsequent update.
233 		 */
234 		pmde = pmdp_get_lockless(pvmw->pmd);
235 
236 		if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde) ||
237 		    (pmd_present(pmde) && pmd_devmap(pmde))) {
238 			pvmw->ptl = pmd_lock(mm, pvmw->pmd);
239 			pmde = *pvmw->pmd;
240 			if (!pmd_present(pmde)) {
241 				swp_entry_t entry;
242 
243 				if (!thp_migration_supported() ||
244 				    !(pvmw->flags & PVMW_MIGRATION))
245 					return not_found(pvmw);
246 				entry = pmd_to_swp_entry(pmde);
247 				if (!is_migration_entry(entry) ||
248 				    !check_pmd(swp_offset_pfn(entry), pvmw))
249 					return not_found(pvmw);
250 				return true;
251 			}
252 			if (likely(pmd_trans_huge(pmde) || pmd_devmap(pmde))) {
253 				if (pvmw->flags & PVMW_MIGRATION)
254 					return not_found(pvmw);
255 				if (!check_pmd(pmd_pfn(pmde), pvmw))
256 					return not_found(pvmw);
257 				return true;
258 			}
259 			/* THP pmd was split under us: handle on pte level */
260 			spin_unlock(pvmw->ptl);
261 			pvmw->ptl = NULL;
262 		} else if (!pmd_present(pmde)) {
263 			/*
264 			 * If PVMW_SYNC, take and drop THP pmd lock so that we
265 			 * cannot return prematurely, while zap_huge_pmd() has
266 			 * cleared *pmd but not decremented compound_mapcount().
267 			 */
268 			if ((pvmw->flags & PVMW_SYNC) &&
269 			    transhuge_vma_suitable(vma, pvmw->address) &&
270 			    (pvmw->nr_pages >= HPAGE_PMD_NR)) {
271 				spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
272 
273 				spin_unlock(ptl);
274 			}
275 			step_forward(pvmw, PMD_SIZE);
276 			continue;
277 		}
278 		if (!map_pte(pvmw, &ptl)) {
279 			if (!pvmw->pte)
280 				goto restart;
281 			goto next_pte;
282 		}
283 this_pte:
284 		if (check_pte(pvmw))
285 			return true;
286 next_pte:
287 		do {
288 			pvmw->address += PAGE_SIZE;
289 			if (pvmw->address >= end)
290 				return not_found(pvmw);
291 			/* Did we cross page table boundary? */
292 			if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
293 				if (pvmw->ptl) {
294 					spin_unlock(pvmw->ptl);
295 					pvmw->ptl = NULL;
296 				}
297 				pte_unmap(pvmw->pte);
298 				pvmw->pte = NULL;
299 				goto restart;
300 			}
301 			pvmw->pte++;
302 		} while (pte_none(ptep_get(pvmw->pte)));
303 
304 		if (!pvmw->ptl) {
305 			pvmw->ptl = ptl;
306 			spin_lock(pvmw->ptl);
307 		}
308 		goto this_pte;
309 	} while (pvmw->address < end);
310 
311 	return false;
312 }
313 
314 /**
315  * page_mapped_in_vma - check whether a page is really mapped in a VMA
316  * @page: the page to test
317  * @vma: the VMA to test
318  *
319  * Returns 1 if the page is mapped into the page tables of the VMA, 0
320  * if the page is not mapped into the page tables of this VMA.  Only
321  * valid for normal file or anonymous VMAs.
322  */
323 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
324 {
325 	struct page_vma_mapped_walk pvmw = {
326 		.pfn = page_to_pfn(page),
327 		.nr_pages = 1,
328 		.vma = vma,
329 		.flags = PVMW_SYNC,
330 	};
331 
332 	pvmw.address = vma_address(page, vma);
333 	if (pvmw.address == -EFAULT)
334 		return 0;
335 	if (!page_vma_mapped_walk(&pvmw))
336 		return 0;
337 	page_vma_mapped_walk_done(&pvmw);
338 	return 1;
339 }
340