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 
not_found(struct page_vma_mapped_walk * pvmw)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 
map_pte(struct page_vma_mapped_walk * pvmw)16 static bool map_pte(struct page_vma_mapped_walk *pvmw)
17 {
18 	pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
19 	if (!(pvmw->flags & PVMW_SYNC)) {
20 		if (pvmw->flags & PVMW_MIGRATION) {
21 			if (!is_swap_pte(*pvmw->pte))
22 				return false;
23 		} else {
24 			/*
25 			 * We get here when we are trying to unmap a private
26 			 * device page from the process address space. Such
27 			 * page is not CPU accessible and thus is mapped as
28 			 * a special swap entry, nonetheless it still does
29 			 * count as a valid regular mapping for the page (and
30 			 * is accounted as such in page maps count).
31 			 *
32 			 * So handle this special case as if it was a normal
33 			 * page mapping ie lock CPU page table and returns
34 			 * true.
35 			 *
36 			 * For more details on device private memory see HMM
37 			 * (include/linux/hmm.h or mm/hmm.c).
38 			 */
39 			if (is_swap_pte(*pvmw->pte)) {
40 				swp_entry_t entry;
41 
42 				/* Handle un-addressable ZONE_DEVICE memory */
43 				entry = pte_to_swp_entry(*pvmw->pte);
44 				if (!is_device_private_entry(entry) &&
45 				    !is_device_exclusive_entry(entry))
46 					return false;
47 			} else if (!pte_present(*pvmw->pte))
48 				return false;
49 		}
50 	}
51 	pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
52 	spin_lock(pvmw->ptl);
53 	return true;
54 }
55 
pfn_is_match(struct page * page,unsigned long pfn)56 static inline bool pfn_is_match(struct page *page, unsigned long pfn)
57 {
58 	unsigned long page_pfn = page_to_pfn(page);
59 
60 	/* normal page and hugetlbfs page */
61 	if (!PageTransCompound(page) || PageHuge(page))
62 		return page_pfn == pfn;
63 
64 	/* THP can be referenced by any subpage */
65 	return pfn >= page_pfn && pfn - page_pfn < thp_nr_pages(page);
66 }
67 
68 /**
69  * check_pte - check if @pvmw->page is mapped at the @pvmw->pte
70  * @pvmw: page_vma_mapped_walk struct, includes a pair pte and page for checking
71  *
72  * page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
73  * mapped. check_pte() has to validate this.
74  *
75  * pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
76  * arbitrary page.
77  *
78  * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
79  * entry that points to @pvmw->page or any subpage in case of THP.
80  *
81  * If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
82  * pvmw->page or any subpage in case of THP.
83  *
84  * Otherwise, return false.
85  *
86  */
check_pte(struct page_vma_mapped_walk * pvmw)87 static bool check_pte(struct page_vma_mapped_walk *pvmw)
88 {
89 	unsigned long pfn;
90 
91 	if (pvmw->flags & PVMW_MIGRATION) {
92 		swp_entry_t entry;
93 		if (!is_swap_pte(*pvmw->pte))
94 			return false;
95 		entry = pte_to_swp_entry(*pvmw->pte);
96 
97 		if (!is_migration_entry(entry) &&
98 		    !is_device_exclusive_entry(entry))
99 			return false;
100 
101 		pfn = swp_offset(entry);
102 	} else if (is_swap_pte(*pvmw->pte)) {
103 		swp_entry_t entry;
104 
105 		/* Handle un-addressable ZONE_DEVICE memory */
106 		entry = pte_to_swp_entry(*pvmw->pte);
107 		if (!is_device_private_entry(entry) &&
108 		    !is_device_exclusive_entry(entry))
109 			return false;
110 
111 		pfn = swp_offset(entry);
112 	} else {
113 		if (!pte_present(*pvmw->pte))
114 			return false;
115 
116 		pfn = pte_pfn(*pvmw->pte);
117 	}
118 
119 	return pfn_is_match(pvmw->page, pfn);
120 }
121 
step_forward(struct page_vma_mapped_walk * pvmw,unsigned long size)122 static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
123 {
124 	pvmw->address = (pvmw->address + size) & ~(size - 1);
125 	if (!pvmw->address)
126 		pvmw->address = ULONG_MAX;
127 }
128 
129 /**
130  * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
131  * @pvmw->address
132  * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
133  * must be set. pmd, pte and ptl must be NULL.
134  *
135  * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
136  * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
137  * adjusted if needed (for PTE-mapped THPs).
138  *
139  * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
140  * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
141  * a loop to find all PTEs that map the THP.
142  *
143  * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
144  * regardless of which page table level the page is mapped at. @pvmw->pmd is
145  * NULL.
146  *
147  * Returns false if there are no more page table entries for the page in
148  * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
149  *
150  * If you need to stop the walk before page_vma_mapped_walk() returned false,
151  * use page_vma_mapped_walk_done(). It will do the housekeeping.
152  */
page_vma_mapped_walk(struct page_vma_mapped_walk * pvmw)153 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
154 {
155 	struct mm_struct *mm = pvmw->vma->vm_mm;
156 	struct page *page = pvmw->page;
157 	unsigned long end;
158 	pgd_t *pgd;
159 	p4d_t *p4d;
160 	pud_t *pud;
161 	pmd_t pmde;
162 
163 	/* The only possible pmd mapping has been handled on last iteration */
164 	if (pvmw->pmd && !pvmw->pte)
165 		return not_found(pvmw);
166 
167 	if (unlikely(PageHuge(page))) {
168 		/* The only possible mapping was handled on last iteration */
169 		if (pvmw->pte)
170 			return not_found(pvmw);
171 
172 		/* when pud is not present, pte will be NULL */
173 		pvmw->pte = huge_pte_offset(mm, pvmw->address, page_size(page));
174 		if (!pvmw->pte)
175 			return false;
176 
177 		pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
178 		spin_lock(pvmw->ptl);
179 		if (!check_pte(pvmw))
180 			return not_found(pvmw);
181 		return true;
182 	}
183 
184 	/*
185 	 * Seek to next pte only makes sense for THP.
186 	 * But more important than that optimization, is to filter out
187 	 * any PageKsm page: whose page->index misleads vma_address()
188 	 * and vma_address_end() to disaster.
189 	 */
190 	end = PageTransCompound(page) ?
191 		vma_address_end(page, pvmw->vma) :
192 		pvmw->address + PAGE_SIZE;
193 	if (pvmw->pte)
194 		goto next_pte;
195 restart:
196 	do {
197 		pgd = pgd_offset(mm, pvmw->address);
198 		if (!pgd_present(*pgd)) {
199 			step_forward(pvmw, PGDIR_SIZE);
200 			continue;
201 		}
202 		p4d = p4d_offset(pgd, pvmw->address);
203 		if (!p4d_present(*p4d)) {
204 			step_forward(pvmw, P4D_SIZE);
205 			continue;
206 		}
207 		pud = pud_offset(p4d, pvmw->address);
208 		if (!pud_present(*pud)) {
209 			step_forward(pvmw, PUD_SIZE);
210 			continue;
211 		}
212 
213 		pvmw->pmd = pmd_offset(pud, pvmw->address);
214 		/*
215 		 * Make sure the pmd value isn't cached in a register by the
216 		 * compiler and used as a stale value after we've observed a
217 		 * subsequent update.
218 		 */
219 		pmde = READ_ONCE(*pvmw->pmd);
220 
221 		if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
222 			pvmw->ptl = pmd_lock(mm, pvmw->pmd);
223 			pmde = *pvmw->pmd;
224 			if (likely(pmd_trans_huge(pmde))) {
225 				if (pvmw->flags & PVMW_MIGRATION)
226 					return not_found(pvmw);
227 				if (pmd_page(pmde) != page)
228 					return not_found(pvmw);
229 				return true;
230 			}
231 			if (!pmd_present(pmde)) {
232 				swp_entry_t entry;
233 
234 				if (!thp_migration_supported() ||
235 				    !(pvmw->flags & PVMW_MIGRATION))
236 					return not_found(pvmw);
237 				entry = pmd_to_swp_entry(pmde);
238 				if (!is_migration_entry(entry) ||
239 				    pfn_swap_entry_to_page(entry) != page)
240 					return not_found(pvmw);
241 				return true;
242 			}
243 			/* THP pmd was split under us: handle on pte level */
244 			spin_unlock(pvmw->ptl);
245 			pvmw->ptl = NULL;
246 		} else if (!pmd_present(pmde)) {
247 			/*
248 			 * If PVMW_SYNC, take and drop THP pmd lock so that we
249 			 * cannot return prematurely, while zap_huge_pmd() has
250 			 * cleared *pmd but not decremented compound_mapcount().
251 			 */
252 			if ((pvmw->flags & PVMW_SYNC) &&
253 			    PageTransCompound(page)) {
254 				spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
255 
256 				spin_unlock(ptl);
257 			}
258 			step_forward(pvmw, PMD_SIZE);
259 			continue;
260 		}
261 		if (!map_pte(pvmw))
262 			goto next_pte;
263 this_pte:
264 		if (check_pte(pvmw))
265 			return true;
266 next_pte:
267 		do {
268 			pvmw->address += PAGE_SIZE;
269 			if (pvmw->address >= end)
270 				return not_found(pvmw);
271 			/* Did we cross page table boundary? */
272 			if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
273 				if (pvmw->ptl) {
274 					spin_unlock(pvmw->ptl);
275 					pvmw->ptl = NULL;
276 				}
277 				pte_unmap(pvmw->pte);
278 				pvmw->pte = NULL;
279 				goto restart;
280 			}
281 			pvmw->pte++;
282 			if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) {
283 				pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
284 				spin_lock(pvmw->ptl);
285 			}
286 		} while (pte_none(*pvmw->pte));
287 
288 		if (!pvmw->ptl) {
289 			pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
290 			spin_lock(pvmw->ptl);
291 		}
292 		goto this_pte;
293 	} while (pvmw->address < end);
294 
295 	return false;
296 }
297 
298 /**
299  * page_mapped_in_vma - check whether a page is really mapped in a VMA
300  * @page: the page to test
301  * @vma: the VMA to test
302  *
303  * Returns 1 if the page is mapped into the page tables of the VMA, 0
304  * if the page is not mapped into the page tables of this VMA.  Only
305  * valid for normal file or anonymous VMAs.
306  */
page_mapped_in_vma(struct page * page,struct vm_area_struct * vma)307 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
308 {
309 	struct page_vma_mapped_walk pvmw = {
310 		.page = page,
311 		.vma = vma,
312 		.flags = PVMW_SYNC,
313 	};
314 
315 	pvmw.address = vma_address(page, vma);
316 	if (pvmw.address == -EFAULT)
317 		return 0;
318 	if (!page_vma_mapped_walk(&pvmw))
319 		return 0;
320 	page_vma_mapped_walk_done(&pvmw);
321 	return 1;
322 }
323