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)
 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
 55static 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 */
 81static 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 */
138bool 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, page_size(page));
157		if (!pvmw->pte)
158			return false;
159
160		pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
161		spin_lock(pvmw->ptl);
162		if (!check_pte(pvmw))
163			return not_found(pvmw);
164		return true;
165	}
166restart:
167	pgd = pgd_offset(mm, pvmw->address);
168	if (!pgd_present(*pgd))
169		return false;
170	p4d = p4d_offset(pgd, pvmw->address);
171	if (!p4d_present(*p4d))
172		return false;
173	pud = pud_offset(p4d, pvmw->address);
174	if (!pud_present(*pud))
175		return false;
176	pvmw->pmd = pmd_offset(pud, pvmw->address);
177	/*
178	 * Make sure the pmd value isn't cached in a register by the
179	 * compiler and used as a stale value after we've observed a
180	 * subsequent update.
181	 */
182	pmde = READ_ONCE(*pvmw->pmd);
183	if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
184		pvmw->ptl = pmd_lock(mm, pvmw->pmd);
185		if (likely(pmd_trans_huge(*pvmw->pmd))) {
186			if (pvmw->flags & PVMW_MIGRATION)
187				return not_found(pvmw);
188			if (pmd_page(*pvmw->pmd) != page)
189				return not_found(pvmw);
190			return true;
191		} else if (!pmd_present(*pvmw->pmd)) {
192			if (thp_migration_supported()) {
193				if (!(pvmw->flags & PVMW_MIGRATION))
194					return not_found(pvmw);
195				if (is_migration_entry(pmd_to_swp_entry(*pvmw->pmd))) {
196					swp_entry_t entry = pmd_to_swp_entry(*pvmw->pmd);
197
198					if (migration_entry_to_page(entry) != page)
199						return not_found(pvmw);
200					return true;
201				}
202			}
203			return not_found(pvmw);
204		} else {
205			/* THP pmd was split under us: handle on pte level */
206			spin_unlock(pvmw->ptl);
207			pvmw->ptl = NULL;
208		}
209	} else if (!pmd_present(pmde)) {
210		return false;
211	}
212	if (!map_pte(pvmw))
213		goto next_pte;
214	while (1) {
215		if (check_pte(pvmw))
216			return true;
217next_pte:
218		/* Seek to next pte only makes sense for THP */
219		if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
220			return not_found(pvmw);
221		do {
222			pvmw->address += PAGE_SIZE;
223			if (pvmw->address >= pvmw->vma->vm_end ||
224			    pvmw->address >=
225					__vma_address(pvmw->page, pvmw->vma) +
226					hpage_nr_pages(pvmw->page) * PAGE_SIZE)
227				return not_found(pvmw);
228			/* Did we cross page table boundary? */
229			if (pvmw->address % PMD_SIZE == 0) {
230				pte_unmap(pvmw->pte);
231				if (pvmw->ptl) {
232					spin_unlock(pvmw->ptl);
233					pvmw->ptl = NULL;
234				}
235				goto restart;
236			} else {
237				pvmw->pte++;
238			}
239		} while (pte_none(*pvmw->pte));
240
241		if (!pvmw->ptl) {
242			pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
243			spin_lock(pvmw->ptl);
244		}
245	}
246}
247
248/**
249 * page_mapped_in_vma - check whether a page is really mapped in a VMA
250 * @page: the page to test
251 * @vma: the VMA to test
252 *
253 * Returns 1 if the page is mapped into the page tables of the VMA, 0
254 * if the page is not mapped into the page tables of this VMA.  Only
255 * valid for normal file or anonymous VMAs.
256 */
257int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
258{
259	struct page_vma_mapped_walk pvmw = {
260		.page = page,
261		.vma = vma,
262		.flags = PVMW_SYNC,
263	};
264	unsigned long start, end;
265
266	start = __vma_address(page, vma);
267	end = start + PAGE_SIZE * (hpage_nr_pages(page) - 1);
268
269	if (unlikely(end < vma->vm_start || start >= vma->vm_end))
270		return 0;
271	pvmw.address = max(start, vma->vm_start);
272	if (!page_vma_mapped_walk(&pvmw))
273		return 0;
274	page_vma_mapped_walk_done(&pvmw);
275	return 1;
276}