* + mm-page_vma_mapped-fix-device-private-pmd-handling.patch added to mm-hotfixes-unstable branch
@ 2026-06-25 21:07 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-06-25 21:07 UTC (permalink / raw)
To: mm-commits, ziy, vbabka, stable, sj, riel, ljs, liam, lance.yang,
jannh, harry, david, balbirs, richard.weiyang, akpm
The patch titled
Subject: mm/page_vma_mapped: fix device-private PMD handling
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-page_vma_mapped-fix-device-private-pmd-handling.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_vma_mapped-fix-device-private-pmd-handling.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
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c) Ideally: find the original patch on the mailing list and do a
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Wei Yang <richard.weiyang@gmail.com>
Subject: mm/page_vma_mapped: fix device-private PMD handling
Date: Wed, 24 Jun 2026 06:53:53 +0000
Commit 65edfda6f3f2 ("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 146287290023 ("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
PVMW_MIGRATION is not set and checks whether a split raced us we do for
PMD THP and migration entries.
Link: https://lore.kernel.org/20260624065353.1622-1-richard.weiyang@gmail.com
Fixes: 65edfda6f3f2 ("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>
Suggested-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/page_vma_mapped.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
--- a/mm/page_vma_mapped.c~mm-page_vma_mapped-fix-device-private-pmd-handling
+++ a/mm/page_vma_mapped.c
@@ -269,14 +269,24 @@ restart:
/* THP 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);
+ } else if (pmd_is_device_private_entry(pmde)) {
+ softleaf_t entry;
+
+ pvmw->ptl = pmd_lock(mm, pvmw->pmd);
+ pmde = *pvmw->pmd;
+ entry = softleaf_from_pmd(pmde);
- if (softleaf_is_device_private(entry)) {
- pvmw->ptl = pmd_lock(mm, pvmw->pmd);
+ if (likely(softleaf_is_device_private(entry))) {
+ if (pvmw->flags & PVMW_MIGRATION)
+ return not_found(pvmw);
+ if (!check_pmd(softleaf_to_pfn(entry), pvmw))
+ return not_found(pvmw);
return true;
}
-
+ /* device-private pmd was split under us: handle on pte level */
+ spin_unlock(pvmw->ptl);
+ pvmw->ptl = NULL;
+ } else if (!pmd_present(pmde)) {
if ((pvmw->flags & PVMW_SYNC) &&
thp_vma_suitable_order(vma, pvmw->address,
PMD_ORDER) &&
_
Patches currently in -mm which might be from richard.weiyang@gmail.com are
mm-page_vma_mapped-fix-device-private-pmd-handling.patch
^ permalink raw reply [flat|nested] 2+ messages in thread* + mm-page_vma_mapped-fix-device-private-pmd-handling.patch added to mm-hotfixes-unstable branch
@ 2026-06-30 2:25 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2026-06-30 2:25 UTC (permalink / raw)
To: mm-commits, ziy, stable, sj, ljs, lance.yang, david, balbirs,
richard.weiyang, akpm
The patch titled
Subject: mm/page_vma_mapped: fix device-private PMD handling
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-page_vma_mapped-fix-device-private-pmd-handling.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_vma_mapped-fix-device-private-pmd-handling.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days
------------------------------------------------------
From: Wei Yang <richard.weiyang@gmail.com>
Subject: mm/page_vma_mapped: fix device-private PMD handling
Date: Tue, 30 Jun 2026 02:15:40 +0000
Commit 65edfda6f3f2 ("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 146287290023 ("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().
Link: https://lore.kernel.org/20260630021540.17297-1-richard.weiyang@gmail.com
Fixes: 65edfda6f3f2 ("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>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/page_vma_mapped.c | 30 ++++++++++++++++--------------
1 file changed, 16 insertions(+), 14 deletions(-)
--- a/mm/page_vma_mapped.c~mm-page_vma_mapped-fix-device-private-pmd-handling
+++ a/mm/page_vma_mapped.c
@@ -243,21 +243,30 @@ restart:
*/
pmde = pmdp_get_lockless(pvmw->pmd);
- if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde)) {
+ if (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 (!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 (!softleaf_is_migration(entry) ||
- !check_pmd(softleaf_to_pfn(entry), pvmw))
+ 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 +275,10 @@ restart:
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) &&
_
Patches currently in -mm which might be from richard.weiyang@gmail.com are
mm-page_vma_mapped-fix-device-private-pmd-handling.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
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