linux/mm/page_vma_mapped.c
Hugh Dickins a7a69d8ba8 mm/thp: another PVMW_SYNC fix in page_vma_mapped_walk()
Aha! Shouldn't that quick scan over pte_none()s make sure that it holds
ptlock in the PVMW_SYNC case? That too might have been responsible for
BUGs or WARNs in split_huge_page_to_list() or its unmap_page(), though
I've never seen any.

Link: https://lkml.kernel.org/r/1bdf384c-8137-a149-2a1e-475a4791c3c@google.com
Link: https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@e16-tech.com/
Fixes: ace71a19ce ("mm: introduce page_vma_mapped_walk()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Wang Yugui <wangyugui@e16-tech.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-24 19:40:53 -07:00

320 lines
8.6 KiB
C

// SPDX-License-Identifier: GPL-2.0
#include <linux/mm.h>
#include <linux/rmap.h>
#include <linux/hugetlb.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include "internal.h"
static inline bool not_found(struct page_vma_mapped_walk *pvmw)
{
page_vma_mapped_walk_done(pvmw);
return false;
}
static bool map_pte(struct page_vma_mapped_walk *pvmw)
{
pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
if (!(pvmw->flags & PVMW_SYNC)) {
if (pvmw->flags & PVMW_MIGRATION) {
if (!is_swap_pte(*pvmw->pte))
return false;
} else {
/*
* We get here when we are trying to unmap a private
* device page from the process address space. Such
* page is not CPU accessible and thus is mapped as
* a special swap entry, nonetheless it still does
* count as a valid regular mapping for the page (and
* is accounted as such in page maps count).
*
* So handle this special case as if it was a normal
* page mapping ie lock CPU page table and returns
* true.
*
* For more details on device private memory see HMM
* (include/linux/hmm.h or mm/hmm.c).
*/
if (is_swap_pte(*pvmw->pte)) {
swp_entry_t entry;
/* Handle un-addressable ZONE_DEVICE memory */
entry = pte_to_swp_entry(*pvmw->pte);
if (!is_device_private_entry(entry))
return false;
} else if (!pte_present(*pvmw->pte))
return false;
}
}
pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
spin_lock(pvmw->ptl);
return true;
}
static inline bool pfn_is_match(struct page *page, unsigned long pfn)
{
unsigned long page_pfn = page_to_pfn(page);
/* normal page and hugetlbfs page */
if (!PageTransCompound(page) || PageHuge(page))
return page_pfn == pfn;
/* THP can be referenced by any subpage */
return pfn >= page_pfn && pfn - page_pfn < thp_nr_pages(page);
}
/**
* check_pte - check if @pvmw->page is mapped at the @pvmw->pte
* @pvmw: page_vma_mapped_walk struct, includes a pair pte and page for checking
*
* page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
* mapped. check_pte() has to validate this.
*
* pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
* arbitrary page.
*
* If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
* entry that points to @pvmw->page or any subpage in case of THP.
*
* If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
* pvmw->page or any subpage in case of THP.
*
* Otherwise, return false.
*
*/
static bool check_pte(struct page_vma_mapped_walk *pvmw)
{
unsigned long pfn;
if (pvmw->flags & PVMW_MIGRATION) {
swp_entry_t entry;
if (!is_swap_pte(*pvmw->pte))
return false;
entry = pte_to_swp_entry(*pvmw->pte);
if (!is_migration_entry(entry))
return false;
pfn = migration_entry_to_pfn(entry);
} else if (is_swap_pte(*pvmw->pte)) {
swp_entry_t entry;
/* Handle un-addressable ZONE_DEVICE memory */
entry = pte_to_swp_entry(*pvmw->pte);
if (!is_device_private_entry(entry))
return false;
pfn = device_private_entry_to_pfn(entry);
} else {
if (!pte_present(*pvmw->pte))
return false;
pfn = pte_pfn(*pvmw->pte);
}
return pfn_is_match(pvmw->page, pfn);
}
static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
{
pvmw->address = (pvmw->address + size) & ~(size - 1);
if (!pvmw->address)
pvmw->address = ULONG_MAX;
}
/**
* page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
* @pvmw->address
* @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
* must be set. pmd, pte and ptl must be NULL.
*
* Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
* to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
* adjusted if needed (for PTE-mapped THPs).
*
* If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
* (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
* a loop to find all PTEs that map the THP.
*
* For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
* regardless of which page table level the page is mapped at. @pvmw->pmd is
* NULL.
*
* Returns false if there are no more page table entries for the page in
* the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
*
* If you need to stop the walk before page_vma_mapped_walk() returned false,
* use page_vma_mapped_walk_done(). It will do the housekeeping.
*/
bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
{
struct mm_struct *mm = pvmw->vma->vm_mm;
struct page *page = pvmw->page;
unsigned long end;
pgd_t *pgd;
p4d_t *p4d;
pud_t *pud;
pmd_t pmde;
/* The only possible pmd mapping has been handled on last iteration */
if (pvmw->pmd && !pvmw->pte)
return not_found(pvmw);
if (unlikely(PageHuge(page))) {
/* The only possible mapping was handled on last iteration */
if (pvmw->pte)
return not_found(pvmw);
/* when pud is not present, pte will be NULL */
pvmw->pte = huge_pte_offset(mm, pvmw->address, page_size(page));
if (!pvmw->pte)
return false;
pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
spin_lock(pvmw->ptl);
if (!check_pte(pvmw))
return not_found(pvmw);
return true;
}
/*
* Seek to next pte only makes sense for THP.
* But more important than that optimization, is to filter out
* any PageKsm page: whose page->index misleads vma_address()
* and vma_address_end() to disaster.
*/
end = PageTransCompound(page) ?
vma_address_end(page, pvmw->vma) :
pvmw->address + PAGE_SIZE;
if (pvmw->pte)
goto next_pte;
restart:
do {
pgd = pgd_offset(mm, pvmw->address);
if (!pgd_present(*pgd)) {
step_forward(pvmw, PGDIR_SIZE);
continue;
}
p4d = p4d_offset(pgd, pvmw->address);
if (!p4d_present(*p4d)) {
step_forward(pvmw, P4D_SIZE);
continue;
}
pud = pud_offset(p4d, pvmw->address);
if (!pud_present(*pud)) {
step_forward(pvmw, PUD_SIZE);
continue;
}
pvmw->pmd = pmd_offset(pud, pvmw->address);
/*
* Make sure the pmd value isn't cached in a register by the
* compiler and used as a stale value after we've observed a
* subsequent update.
*/
pmde = READ_ONCE(*pvmw->pmd);
if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
pvmw->ptl = pmd_lock(mm, pvmw->pmd);
pmde = *pvmw->pmd;
if (likely(pmd_trans_huge(pmde))) {
if (pvmw->flags & PVMW_MIGRATION)
return not_found(pvmw);
if (pmd_page(pmde) != page)
return not_found(pvmw);
return true;
}
if (!pmd_present(pmde)) {
swp_entry_t entry;
if (!thp_migration_supported() ||
!(pvmw->flags & PVMW_MIGRATION))
return not_found(pvmw);
entry = pmd_to_swp_entry(pmde);
if (!is_migration_entry(entry) ||
migration_entry_to_page(entry) != page)
return not_found(pvmw);
return true;
}
/* THP pmd was split under us: handle on pte level */
spin_unlock(pvmw->ptl);
pvmw->ptl = NULL;
} else if (!pmd_present(pmde)) {
/*
* If PVMW_SYNC, take and drop THP pmd lock so that we
* cannot return prematurely, while zap_huge_pmd() has
* cleared *pmd but not decremented compound_mapcount().
*/
if ((pvmw->flags & PVMW_SYNC) &&
PageTransCompound(page)) {
spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
spin_unlock(ptl);
}
step_forward(pvmw, PMD_SIZE);
continue;
}
if (!map_pte(pvmw))
goto next_pte;
this_pte:
if (check_pte(pvmw))
return true;
next_pte:
do {
pvmw->address += PAGE_SIZE;
if (pvmw->address >= end)
return not_found(pvmw);
/* Did we cross page table boundary? */
if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
if (pvmw->ptl) {
spin_unlock(pvmw->ptl);
pvmw->ptl = NULL;
}
pte_unmap(pvmw->pte);
pvmw->pte = NULL;
goto restart;
}
pvmw->pte++;
if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) {
pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
spin_lock(pvmw->ptl);
}
} while (pte_none(*pvmw->pte));
if (!pvmw->ptl) {
pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
spin_lock(pvmw->ptl);
}
goto this_pte;
} while (pvmw->address < end);
return false;
}
/**
* page_mapped_in_vma - check whether a page is really mapped in a VMA
* @page: the page to test
* @vma: the VMA to test
*
* Returns 1 if the page is mapped into the page tables of the VMA, 0
* if the page is not mapped into the page tables of this VMA. Only
* valid for normal file or anonymous VMAs.
*/
int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
{
struct page_vma_mapped_walk pvmw = {
.page = page,
.vma = vma,
.flags = PVMW_SYNC,
};
pvmw.address = vma_address(page, vma);
if (pvmw.address == -EFAULT)
return 0;
if (!page_vma_mapped_walk(&pvmw))
return 0;
page_vma_mapped_walk_done(&pvmw);
return 1;
}