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mm/page_vma_mapped: fix device-private PMD handling

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Commit 65edfda6f3 ("mm/rmap: extend rmap and migration support
device-private entries") introduced the concept of device-private PMD
entries, but did not correctly update the rmap walk code to account for
them.

As a result, when page_vma_mapped_walk() encounters device-private PMD
entries, it takes no action other than to acquire the PMD lock and exit.

However this is highly problematic for two reasons - firstly, device
private entries possess a PFN so check_pmd() needs to be called to ensure
an overlapping PFN range.

Secondly, and more importantly, if PVMW_MIGRATION is set the caller
assumes the returned entry is a migration entry, resulting in memory
corruption when the caller tries to interpret the device private entry as
such.

In addition, commit 1462872900 ("mm/huge_memory: implement
device-private THP splitting") allowed device private PMDs to be split
like THP mappings, but again did not update this code path.

As a result, we might race a PMD split prior to acquiring the PMD lock.

This patch addresses all of these issues by invoking check_pmd(), ensuring
PMVW_MIGRATION is not set and checks whether a split raced us we do for
PMD THP and migration entries.

Instead of checking for a subset of the cases after taking the pmd_lock(),
put device-private along with pmd_trans_huge() and
pmd_is_migration_entry().  Also remove thp_migration_supported() as it is
already guarded by pmd_is_migration_entry().

[akpm@linux-foundation.org: fix Raspberry Pi 1 build, per David]
Link: https://lore.kernel.org/20260630021540.17297-1-richard.weiyang@gmail.com
Fixes: 65edfda6f3 ("mm/rmap: extend rmap and migration support device-private entries")
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Suggested-by: David Hildenbrand <david@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Acked-by: Balbir Singh <balbirs@nvidia.com>
Tested-by: Klara Modin <klarasmodin@gmail.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: <stable@vger.kernel.org>q
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Wei Yang
2026-06-30 02:15:40 +00:00
committed by Andrew Morton
parent 14afcf67dc
commit f84ca9b188
1 changed files with 18 additions and 15 deletions
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33
mm/page_vma_mapped.c
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@@ -243,21 +243,31 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
*/
pmde = pmdp_get_lockless(pvmw->pmd);
if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde)) {
if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
(pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) ||
pmd_is_device_private_entry(pmde))) {
pvmw->ptl = pmd_lock(mm, pvmw->pmd);
pmde = *pvmw->pmd;
if (!pmd_present(pmde)) {
if (pmd_is_migration_entry(pmde)) {
softleaf_t entry;
if (!thp_migration_supported() ||
!(pvmw->flags & PVMW_MIGRATION))
if (!(pvmw->flags & PVMW_MIGRATION))
return not_found(pvmw);
entry = softleaf_from_pmd(pmde);
if (!softleaf_is_migration(entry) ||
!check_pmd(softleaf_to_pfn(entry), pvmw))
if (!check_pmd(softleaf_to_pfn(entry), pvmw))
return not_found(pvmw);
return true;
} else if (pmd_is_device_private_entry(pmde)) {
softleaf_t entry;
if (pvmw->flags & PVMW_MIGRATION)
return not_found(pvmw);
entry = softleaf_from_pmd(pmde);
if (!check_pmd(softleaf_to_pfn(entry), pvmw))
return not_found(pvmw);
return true;
} else if (!pmd_present(pmde)) {
return not_found(pvmw);
}
if (likely(pmd_trans_huge(pmde))) {
if (pvmw->flags & PVMW_MIGRATION)
@@ -266,17 +276,10 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
return not_found(pvmw);
return true;
}
/* THP pmd was split under us: handle on pte level */
/* THP/device-private pmd was split under us: handle on pte level */
spin_unlock(pvmw->ptl);
pvmw->ptl = NULL;
} else if (!pmd_present(pmde)) {
const softleaf_t entry = softleaf_from_pmd(pmde);
if (softleaf_is_device_private(entry)) {
pvmw->ptl = pmd_lock(mm, pvmw->pmd);
return true;
}
if ((pvmw->flags & PVMW_SYNC) &&
thp_vma_suitable_order(vma, pvmw->address,
PMD_ORDER) &&