xref: /openbmc/linux/mm/page_vma_mapped.c (revision b8d312aa)
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)
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 					return false;
46 			} else if (!pte_present(*pvmw->pte))
47 				return false;
48 		}
49 	}
50 	pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
51 	spin_lock(pvmw->ptl);
52 	return true;
53 }
54 
55 static inline bool pfn_in_hpage(struct page *hpage, unsigned long pfn)
56 {
57 	unsigned long hpage_pfn = page_to_pfn(hpage);
58 
59 	/* THP can be referenced by any subpage */
60 	return pfn >= hpage_pfn && pfn - hpage_pfn < hpage_nr_pages(hpage);
61 }
62 
63 /**
64  * check_pte - check if @pvmw->page is mapped at the @pvmw->pte
65  *
66  * page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
67  * mapped. check_pte() has to validate this.
68  *
69  * @pvmw->pte may point to empty PTE, swap PTE or PTE pointing to arbitrary
70  * page.
71  *
72  * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
73  * entry that points to @pvmw->page or any subpage in case of THP.
74  *
75  * If PVMW_MIGRATION flag is not set, returns true if @pvmw->pte points to
76  * @pvmw->page or any subpage in case of THP.
77  *
78  * Otherwise, return false.
79  *
80  */
81 static bool check_pte(struct page_vma_mapped_walk *pvmw)
82 {
83 	unsigned long pfn;
84 
85 	if (pvmw->flags & PVMW_MIGRATION) {
86 		swp_entry_t entry;
87 		if (!is_swap_pte(*pvmw->pte))
88 			return false;
89 		entry = pte_to_swp_entry(*pvmw->pte);
90 
91 		if (!is_migration_entry(entry))
92 			return false;
93 
94 		pfn = migration_entry_to_pfn(entry);
95 	} else if (is_swap_pte(*pvmw->pte)) {
96 		swp_entry_t entry;
97 
98 		/* Handle un-addressable ZONE_DEVICE memory */
99 		entry = pte_to_swp_entry(*pvmw->pte);
100 		if (!is_device_private_entry(entry))
101 			return false;
102 
103 		pfn = device_private_entry_to_pfn(entry);
104 	} else {
105 		if (!pte_present(*pvmw->pte))
106 			return false;
107 
108 		pfn = pte_pfn(*pvmw->pte);
109 	}
110 
111 	return pfn_in_hpage(pvmw->page, pfn);
112 }
113 
114 /**
115  * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
116  * @pvmw->address
117  * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
118  * must be set. pmd, pte and ptl must be NULL.
119  *
120  * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
121  * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
122  * adjusted if needed (for PTE-mapped THPs).
123  *
124  * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
125  * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
126  * a loop to find all PTEs that map the THP.
127  *
128  * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
129  * regardless of which page table level the page is mapped at. @pvmw->pmd is
130  * NULL.
131  *
132  * Retruns false if there are no more page table entries for the page in
133  * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
134  *
135  * If you need to stop the walk before page_vma_mapped_walk() returned false,
136  * use page_vma_mapped_walk_done(). It will do the housekeeping.
137  */
138 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
139 {
140 	struct mm_struct *mm = pvmw->vma->vm_mm;
141 	struct page *page = pvmw->page;
142 	pgd_t *pgd;
143 	p4d_t *p4d;
144 	pud_t *pud;
145 	pmd_t pmde;
146 
147 	/* The only possible pmd mapping has been handled on last iteration */
148 	if (pvmw->pmd && !pvmw->pte)
149 		return not_found(pvmw);
150 
151 	if (pvmw->pte)
152 		goto next_pte;
153 
154 	if (unlikely(PageHuge(pvmw->page))) {
155 		/* when pud is not present, pte will be NULL */
156 		pvmw->pte = huge_pte_offset(mm, pvmw->address,
157 					    PAGE_SIZE << compound_order(page));
158 		if (!pvmw->pte)
159 			return false;
160 
161 		pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
162 		spin_lock(pvmw->ptl);
163 		if (!check_pte(pvmw))
164 			return not_found(pvmw);
165 		return true;
166 	}
167 restart:
168 	pgd = pgd_offset(mm, pvmw->address);
169 	if (!pgd_present(*pgd))
170 		return false;
171 	p4d = p4d_offset(pgd, pvmw->address);
172 	if (!p4d_present(*p4d))
173 		return false;
174 	pud = pud_offset(p4d, pvmw->address);
175 	if (!pud_present(*pud))
176 		return false;
177 	pvmw->pmd = pmd_offset(pud, pvmw->address);
178 	/*
179 	 * Make sure the pmd value isn't cached in a register by the
180 	 * compiler and used as a stale value after we've observed a
181 	 * subsequent update.
182 	 */
183 	pmde = READ_ONCE(*pvmw->pmd);
184 	if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
185 		pvmw->ptl = pmd_lock(mm, pvmw->pmd);
186 		if (likely(pmd_trans_huge(*pvmw->pmd))) {
187 			if (pvmw->flags & PVMW_MIGRATION)
188 				return not_found(pvmw);
189 			if (pmd_page(*pvmw->pmd) != page)
190 				return not_found(pvmw);
191 			return true;
192 		} else if (!pmd_present(*pvmw->pmd)) {
193 			if (thp_migration_supported()) {
194 				if (!(pvmw->flags & PVMW_MIGRATION))
195 					return not_found(pvmw);
196 				if (is_migration_entry(pmd_to_swp_entry(*pvmw->pmd))) {
197 					swp_entry_t entry = pmd_to_swp_entry(*pvmw->pmd);
198 
199 					if (migration_entry_to_page(entry) != page)
200 						return not_found(pvmw);
201 					return true;
202 				}
203 			}
204 			return not_found(pvmw);
205 		} else {
206 			/* THP pmd was split under us: handle on pte level */
207 			spin_unlock(pvmw->ptl);
208 			pvmw->ptl = NULL;
209 		}
210 	} else if (!pmd_present(pmde)) {
211 		return false;
212 	}
213 	if (!map_pte(pvmw))
214 		goto next_pte;
215 	while (1) {
216 		if (check_pte(pvmw))
217 			return true;
218 next_pte:
219 		/* Seek to next pte only makes sense for THP */
220 		if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
221 			return not_found(pvmw);
222 		do {
223 			pvmw->address += PAGE_SIZE;
224 			if (pvmw->address >= pvmw->vma->vm_end ||
225 			    pvmw->address >=
226 					__vma_address(pvmw->page, pvmw->vma) +
227 					hpage_nr_pages(pvmw->page) * PAGE_SIZE)
228 				return not_found(pvmw);
229 			/* Did we cross page table boundary? */
230 			if (pvmw->address % PMD_SIZE == 0) {
231 				pte_unmap(pvmw->pte);
232 				if (pvmw->ptl) {
233 					spin_unlock(pvmw->ptl);
234 					pvmw->ptl = NULL;
235 				}
236 				goto restart;
237 			} else {
238 				pvmw->pte++;
239 			}
240 		} while (pte_none(*pvmw->pte));
241 
242 		if (!pvmw->ptl) {
243 			pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
244 			spin_lock(pvmw->ptl);
245 		}
246 	}
247 }
248 
249 /**
250  * page_mapped_in_vma - check whether a page is really mapped in a VMA
251  * @page: the page to test
252  * @vma: the VMA to test
253  *
254  * Returns 1 if the page is mapped into the page tables of the VMA, 0
255  * if the page is not mapped into the page tables of this VMA.  Only
256  * valid for normal file or anonymous VMAs.
257  */
258 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
259 {
260 	struct page_vma_mapped_walk pvmw = {
261 		.page = page,
262 		.vma = vma,
263 		.flags = PVMW_SYNC,
264 	};
265 	unsigned long start, end;
266 
267 	start = __vma_address(page, vma);
268 	end = start + PAGE_SIZE * (hpage_nr_pages(page) - 1);
269 
270 	if (unlikely(end < vma->vm_start || start >= vma->vm_end))
271 		return 0;
272 	pvmw.address = max(start, vma->vm_start);
273 	if (!page_vma_mapped_walk(&pvmw))
274 		return 0;
275 	page_vma_mapped_walk_done(&pvmw);
276 	return 1;
277 }
278