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