linux-kernel - [PATCH v6.1 1/2] x86/mm/pat: clear VM_PAT if copy_p4d

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Message-Id: <20251224102432.923410-2-ajay.kaher@broadcom.com>
Date: Wed, 24 Dec 2025 10:24:31 +0000
From: Ajay Kaher <ajay.kaher@...adcom.com>
To: stable@...r.kernel.org,
	gregkh@...uxfoundation.org
Cc: dave.hansen@...ux.intel.com,
	luto@...nel.org,
	peterz@...radead.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	hpa@...or.com,
	akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	ajay.kaher@...adcom.com,
	alexey.makhalov@...adcom.com,
	vamsi-krishna.brahmajosyula@...adcom.com,
	yin.ding@...adcom.com,
	tapas.kundu@...adcom.com,
	Ma Wupeng <mawupeng1@...wei.com>,
	syzbot+5f488e922d047d8f00cc@...kaller.appspotmail.com,
	Alexander Ofitserov <oficerovas@...linux.org>
Subject: [PATCH v6.1 1/2] x86/mm/pat: clear VM_PAT if copy_p4d_range failed

From: Ma Wupeng <mawupeng1@...wei.com>

[ Upstream commit d155df53f31068c3340733d586eb9b3ddfd70fc5 ]

Syzbot reports a warning in untrack_pfn().  Digging into the root we found
that this is due to memory allocation failure in pmd_alloc_one.  And this
failure is produced due to failslab.

In copy_page_range(), memory alloaction for pmd failed.  During the error
handling process in copy_page_range(), mmput() is called to remove all
vmas.  While untrack_pfn this empty pfn, warning happens.

Here's a simplified flow:

dup_mm
  dup_mmap
    copy_page_range
      copy_p4d_range
        copy_pud_range
          copy_pmd_range
            pmd_alloc
              __pmd_alloc
                pmd_alloc_one
                  page = alloc_pages(gfp, 0);
                    if (!page)
                      return NULL;
    mmput
        exit_mmap
          unmap_vmas
            unmap_single_vma
              untrack_pfn
                follow_phys
                  WARN_ON_ONCE(1);

Since this vma is not generate successfully, we can clear flag VM_PAT.  In
this case, untrack_pfn() will not be called while cleaning this vma.

Function untrack_pfn_moved() has also been renamed to fit the new logic.

Link: https://lkml.kernel.org/r/20230217025615.1595558-1-mawupeng1@huawei.com
Signed-off-by: Ma Wupeng <mawupeng1@...wei.com>
Reported-by: <syzbot+5f488e922d047d8f00cc@...kaller.appspotmail.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Alexander Ofitserov <oficerovas@...linux.org>
Cc: stable@...r.kernel.org
[ Ajay: Modified to apply on v6.1 ]
Signed-off-by: Ajay Kaher <ajay.kaher@...adcom.com>
---
 arch/x86/mm/pat/memtype.c | 12 ++++++++----
 include/linux/pgtable.h   |  7 ++++---
 mm/memory.c               |  1 +
 mm/mremap.c               |  2 +-
 4 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c
index d6fe9093e..1ad881017 100644
--- a/arch/x86/mm/pat/memtype.c
+++ b/arch/x86/mm/pat/memtype.c
@@ -1137,11 +1137,15 @@ void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
 }
 
 /*
- * untrack_pfn_moved is called, while mremapping a pfnmap for a new region,
- * with the old vma after its pfnmap page table has been removed.  The new
- * vma has a new pfnmap to the same pfn & cache type with VM_PAT set.
+ * untrack_pfn_clear is called if the following situation fits:
+ *
+ * 1) while mremapping a pfnmap for a new region,  with the old vma after
+ * its pfnmap page table has been removed.  The new vma has a new pfnmap
+ * to the same pfn & cache type with VM_PAT set.
+ * 2) while duplicating vm area, the new vma fails to copy the pgtable from
+ * old vma.
  */
-void untrack_pfn_moved(struct vm_area_struct *vma)
+void untrack_pfn_clear(struct vm_area_struct *vma)
 {
 	vma->vm_flags &= ~VM_PAT;
 }
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 82d78cba7..500a612ff 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1214,9 +1214,10 @@ static inline void untrack_pfn(struct vm_area_struct *vma,
 }
 
 /*
- * untrack_pfn_moved is called while mremapping a pfnmap for a new region.
+ * untrack_pfn_clear is called while mremapping a pfnmap for a new region
+ * or fails to copy pgtable during duplicate vm area.
  */
-static inline void untrack_pfn_moved(struct vm_area_struct *vma)
+static inline void untrack_pfn_clear(struct vm_area_struct *vma)
 {
 }
 #else
@@ -1228,7 +1229,7 @@ extern void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot,
 extern int track_pfn_copy(struct vm_area_struct *vma);
 extern void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
 			unsigned long size);
-extern void untrack_pfn_moved(struct vm_area_struct *vma);
+extern void untrack_pfn_clear(struct vm_area_struct *vma);
 #endif
 
 #ifdef CONFIG_MMU
diff --git a/mm/memory.c b/mm/memory.c
index 454d91844..41a03adcf 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1335,6 +1335,7 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
 			continue;
 		if (unlikely(copy_p4d_range(dst_vma, src_vma, dst_pgd, src_pgd,
 					    addr, next))) {
+			untrack_pfn_clear(dst_vma);
 			ret = -ENOMEM;
 			break;
 		}
diff --git a/mm/mremap.c b/mm/mremap.c
index 930f65c31..6ed28eeae 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -682,7 +682,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 
 	/* Tell pfnmap has moved from this vma */
 	if (unlikely(vma->vm_flags & VM_PFNMAP))
-		untrack_pfn_moved(vma);
+		untrack_pfn_clear(vma);
 
 	if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
 		/* We always clear VM_LOCKED[ONFAULT] on the old vma */
-- 
2.40.4