FAILED: patch "[PATCH] mm/memory: fix PMD/PUD checks in follow_pfnmap_start()" failed to apply to 6.12-stable tree

FAILED: patch "[PATCH] mm/memory: fix PMD/PUD checks in follow_pfnmap_start()" failed to apply to 6.12-stable tree

[gregkh]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x ffef67b93aa352b34e6aeba3d52c19a63885409a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026033034-amount-briar-a849@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ffef67b93aa352b34e6aeba3d52c19a63885409a Mon Sep 17 00:00:00 2001
From: "David Hildenbrand (Arm)" <david@kernel.org>
Date: Mon, 23 Mar 2026 21:20:18 +0100
Subject: [PATCH] mm/memory: fix PMD/PUD checks in follow_pfnmap_start()

follow_pfnmap_start() suffers from two problems:

(1) We are not re-fetching the pmd/pud after taking the PTL

Therefore, we are not properly stabilizing what the lock actually
protects.  If there is concurrent zapping, we would indicate to the
caller that we found an entry, however, that entry might already have
been invalidated, or contain a different PFN after taking the lock.

Properly use pmdp_get() / pudp_get() after taking the lock.

(2) pmd_leaf() / pud_leaf() are not well defined on non-present entries

pmd_leaf()/pud_leaf() could wrongly trigger on non-present entries.

There is no real guarantee that pmd_leaf()/pud_leaf() returns something
reasonable on non-present entries.  Most architectures indeed either
perform a present check or make it work by smart use of flags.

However, for example loongarch checks the _PAGE_HUGE flag in pmd_leaf(),
and always sets the _PAGE_HUGE flag in __swp_entry_to_pmd().  Whereby
pmd_trans_huge() explicitly checks pmd_present(), pmd_leaf() does not do
that.

Let's check pmd_present()/pud_present() before assuming "the is a present
PMD leaf" when spotting pmd_leaf()/pud_leaf(), like other page table
handling code that traverses user page tables does.

Given that non-present PMD entries are likely rare in VM_IO|VM_PFNMAP, (1)
is likely more relevant than (2).  It is questionable how often (1) would
actually trigger, but let's CC stable to be sure.

This was found by code inspection.

Link: https://lkml.kernel.org/r/20260323-follow_pfnmap_fix-v1-1-5b0ec10872b3@kernel.org
Fixes: 6da8e9634bb7 ("mm: new follow_pfnmap API")
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index 2f815a34d924..c65e82c86fed 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6815,11 +6815,16 @@ int follow_pfnmap_start(struct follow_pfnmap_args *args)
 
 	pudp = pud_offset(p4dp, address);
 	pud = pudp_get(pudp);
-	if (pud_none(pud))
+	if (!pud_present(pud))
 		goto out;
 	if (pud_leaf(pud)) {
 		lock = pud_lock(mm, pudp);
-		if (!unlikely(pud_leaf(pud))) {
+		pud = pudp_get(pudp);
+
+		if (unlikely(!pud_present(pud))) {
+			spin_unlock(lock);
+			goto out;
+		} else if (unlikely(!pud_leaf(pud))) {
 			spin_unlock(lock);
 			goto retry;
 		}
@@ -6831,9 +6836,16 @@ int follow_pfnmap_start(struct follow_pfnmap_args *args)
 
 	pmdp = pmd_offset(pudp, address);
 	pmd = pmdp_get_lockless(pmdp);
+	if (!pmd_present(pmd))
+		goto out;
 	if (pmd_leaf(pmd)) {
 		lock = pmd_lock(mm, pmdp);
-		if (!unlikely(pmd_leaf(pmd))) {
+		pmd = pmdp_get(pmdp);
+
+		if (unlikely(!pmd_present(pmd))) {
+			spin_unlock(lock);
+			goto out;
+		} else if (unlikely(!pmd_leaf(pmd))) {
 			spin_unlock(lock);
 			goto retry;
 		}

[PATCH 6.12.y 1/2] mm: replace READ_ONCE() with standard page table accessors

[Sasha Levin]

From: Anshuman Khandual <anshuman.khandual@arm.com>

[ Upstream commit c0efdb373c3aaacb32db59cadb0710cac13e44ae ]

Replace all READ_ONCE() with a standard page table accessors i.e
pxdp_get() that defaults into READ_ONCE() in cases where platform does not
override.

Link: https://lkml.kernel.org/r/20251007063100.2396936-1-anshuman.khandual@arm.com
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: ffef67b93aa3 ("mm/memory: fix PMD/PUD checks in follow_pfnmap_start()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/gup.c            | 10 +++++-----
 mm/hmm.c            |  2 +-
 mm/memory.c         |  4 ++--
 mm/mprotect.c       |  2 +-
 mm/sparse-vmemmap.c |  2 +-
 mm/vmscan.c         |  2 +-
 6 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index d105817a0c9aa..937865ecfae00 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1013,7 +1013,7 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma,
 	struct mm_struct *mm = vma->vm_mm;
 
 	pudp = pud_offset(p4dp, address);
-	pud = READ_ONCE(*pudp);
+	pud = pudp_get(pudp);
 	if (!pud_present(pud))
 		return no_page_table(vma, flags, address);
 	if (pud_leaf(pud)) {
@@ -1038,7 +1038,7 @@ static struct page *follow_p4d_mask(struct vm_area_struct *vma,
 	p4d_t *p4dp, p4d;
 
 	p4dp = p4d_offset(pgdp, address);
-	p4d = READ_ONCE(*p4dp);
+	p4d = p4dp_get(p4dp);
 	BUILD_BUG_ON(p4d_leaf(p4d));
 
 	if (!p4d_present(p4d) || p4d_bad(p4d))
@@ -3301,7 +3301,7 @@ static int gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr,
 
 	pudp = pud_offset_lockless(p4dp, p4d, addr);
 	do {
-		pud_t pud = READ_ONCE(*pudp);
+		pud_t pud = pudp_get(pudp);
 
 		next = pud_addr_end(addr, end);
 		if (unlikely(!pud_present(pud)))
@@ -3327,7 +3327,7 @@ static int gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
 
 	p4dp = p4d_offset_lockless(pgdp, pgd, addr);
 	do {
-		p4d_t p4d = READ_ONCE(*p4dp);
+		p4d_t p4d = p4dp_get(p4dp);
 
 		next = p4d_addr_end(addr, end);
 		if (!p4d_present(p4d))
@@ -3349,7 +3349,7 @@ static void gup_fast_pgd_range(unsigned long addr, unsigned long end,
 
 	pgdp = pgd_offset(current->mm, addr);
 	do {
-		pgd_t pgd = READ_ONCE(*pgdp);
+		pgd_t pgd = pgdp_get(pgdp);
 
 		next = pgd_addr_end(addr, end);
 		if (pgd_none(pgd))
diff --git a/mm/hmm.c b/mm/hmm.c
index a67776aeb0199..a27866a1d9bd5 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -423,7 +423,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 	/* Normally we don't want to split the huge page */
 	walk->action = ACTION_CONTINUE;
 
-	pud = READ_ONCE(*pudp);
+	pud = pudp_get(pudp);
 	if (!pud_present(pud)) {
 		spin_unlock(ptl);
 		return hmm_vma_walk_hole(start, end, -1, walk);
diff --git a/mm/memory.c b/mm/memory.c
index 090e9c6f99920..d27cd9a7443ce 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6451,12 +6451,12 @@ int follow_pfnmap_start(struct follow_pfnmap_args *args)
 		goto out;
 
 	p4dp = p4d_offset(pgdp, address);
-	p4d = READ_ONCE(*p4dp);
+	p4d = p4dp_get(p4dp);
 	if (p4d_none(p4d) || unlikely(p4d_bad(p4d)))
 		goto out;
 
 	pudp = pud_offset(p4dp, address);
-	pud = READ_ONCE(*pudp);
+	pud = pudp_get(pudp);
 	if (pud_none(pud))
 		goto out;
 	if (pud_leaf(pud)) {
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 6f450af3252eb..a7c2d7c68a6a5 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -447,7 +447,7 @@ static inline long change_pud_range(struct mmu_gather *tlb,
 			break;
 		}
 
-		pud = READ_ONCE(*pudp);
+		pud = pudp_get(pudp);
 		if (pud_none(pud))
 			continue;
 
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index c3353cd442a5d..3e88708886e37 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -337,7 +337,7 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
 			return -ENOMEM;
 
 		pmd = pmd_offset(pud, addr);
-		if (pmd_none(READ_ONCE(*pmd))) {
+		if (pmd_none(pmdp_get(pmd))) {
 			void *p;
 
 			p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0ceed77af0fbd..deeb4310fd54c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3631,7 +3631,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end,
 	pud = pud_offset(p4d, start & P4D_MASK);
 restart:
 	for (i = pud_index(start), addr = start; addr != end; i++, addr = next) {
-		pud_t val = READ_ONCE(pud[i]);
+		pud_t val = pudp_get(pud + i);
 
 		next = pud_addr_end(addr, end);
 
-- 
2.53.0

[PATCH 6.12.y 2/2] mm/memory: fix PMD/PUD checks in follow_pfnmap_start()

[Sasha Levin]

From: "David Hildenbrand (Arm)" <david@kernel.org>

[ Upstream commit ffef67b93aa352b34e6aeba3d52c19a63885409a ]

follow_pfnmap_start() suffers from two problems:

(1) We are not re-fetching the pmd/pud after taking the PTL

Therefore, we are not properly stabilizing what the lock actually
protects.  If there is concurrent zapping, we would indicate to the
caller that we found an entry, however, that entry might already have
been invalidated, or contain a different PFN after taking the lock.

Properly use pmdp_get() / pudp_get() after taking the lock.

(2) pmd_leaf() / pud_leaf() are not well defined on non-present entries

pmd_leaf()/pud_leaf() could wrongly trigger on non-present entries.

There is no real guarantee that pmd_leaf()/pud_leaf() returns something
reasonable on non-present entries.  Most architectures indeed either
perform a present check or make it work by smart use of flags.

However, for example loongarch checks the _PAGE_HUGE flag in pmd_leaf(),
and always sets the _PAGE_HUGE flag in __swp_entry_to_pmd().  Whereby
pmd_trans_huge() explicitly checks pmd_present(), pmd_leaf() does not do
that.

Let's check pmd_present()/pud_present() before assuming "the is a present
PMD leaf" when spotting pmd_leaf()/pud_leaf(), like other page table
handling code that traverses user page tables does.

Given that non-present PMD entries are likely rare in VM_IO|VM_PFNMAP, (1)
is likely more relevant than (2).  It is questionable how often (1) would
actually trigger, but let's CC stable to be sure.

This was found by code inspection.

Link: https://lkml.kernel.org/r/20260323-follow_pfnmap_fix-v1-1-5b0ec10872b3@kernel.org
Fixes: 6da8e9634bb7 ("mm: new follow_pfnmap API")
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/memory.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index d27cd9a7443ce..49ee03c4392ef 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6457,11 +6457,16 @@ int follow_pfnmap_start(struct follow_pfnmap_args *args)
 
 	pudp = pud_offset(p4dp, address);
 	pud = pudp_get(pudp);
-	if (pud_none(pud))
+	if (!pud_present(pud))
 		goto out;
 	if (pud_leaf(pud)) {
 		lock = pud_lock(mm, pudp);
-		if (!unlikely(pud_leaf(pud))) {
+		pud = pudp_get(pudp);
+
+		if (unlikely(!pud_present(pud))) {
+			spin_unlock(lock);
+			goto out;
+		} else if (unlikely(!pud_leaf(pud))) {
 			spin_unlock(lock);
 			goto retry;
 		}
@@ -6473,9 +6478,16 @@ int follow_pfnmap_start(struct follow_pfnmap_args *args)
 
 	pmdp = pmd_offset(pudp, address);
 	pmd = pmdp_get_lockless(pmdp);
+	if (!pmd_present(pmd))
+		goto out;
 	if (pmd_leaf(pmd)) {
 		lock = pmd_lock(mm, pmdp);
-		if (!unlikely(pmd_leaf(pmd))) {
+		pmd = pmdp_get(pmdp);
+
+		if (unlikely(!pmd_present(pmd))) {
+			spin_unlock(lock);
+			goto out;
+		} else if (unlikely(!pmd_leaf(pmd))) {
 			spin_unlock(lock);
 			goto retry;
 		}
-- 
2.53.0