---
id: CVE-2026-31466
title: 'mm/huge_memory: fix folio isn''t locked in softleaf_to_folio()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  mm/huge_memory: fix folio isn't locked in softleaf_to_folio()

  On arm64 server, we found folio that get from migration entry isn't locked
  in softleaf_to_folio().  This …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b <
    426ee10711586617da869c8bb798214965337617
  - >-
    Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b <
    f1acf5887c2bbaf998dc3fe32c72b7a8b84a3ddd
  - >-
    Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b <
    722cfaf6b31d31123439e67b5deac6b1261a3dea
  - >-
    Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b <
    7ddcf4a245c1c5a91fdd9698757e3d95179ffe41
  - >-
    Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b <
    b8c49ad888892ad7b77062b9c102b799a3e9b4f8
  - >-
    Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b <
    7ad1997b9bc8032603df8f091761114479285769
  - >-
    Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b <
    8bfb8414e9f2ce6f5f2f0e3d0da52f2d132128e7
  - >-
    Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b <
    4c5e7f0fcd592801c9cc18f29f80fbee84eb8669
  - Linux 4.5
published: '2026-04-22'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:47:20.167Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-31466'
references:
  - url: 'https://git.kernel.org/stable/c/426ee10711586617da869c8bb798214965337617'
  - url: 'https://git.kernel.org/stable/c/f1acf5887c2bbaf998dc3fe32c72b7a8b84a3ddd'
  - url: 'https://git.kernel.org/stable/c/722cfaf6b31d31123439e67b5deac6b1261a3dea'
  - url: 'https://git.kernel.org/stable/c/7ddcf4a245c1c5a91fdd9698757e3d95179ffe41'
  - url: 'https://git.kernel.org/stable/c/b8c49ad888892ad7b77062b9c102b799a3e9b4f8'
  - url: 'https://git.kernel.org/stable/c/7ad1997b9bc8032603df8f091761114479285769'
  - url: 'https://git.kernel.org/stable/c/8bfb8414e9f2ce6f5f2f0e3d0da52f2d132128e7'
  - url: 'https://git.kernel.org/stable/c/4c5e7f0fcd592801c9cc18f29f80fbee84eb8669'
tags:
  - cve.org
epss: 0.00117
epssPercentile: 0.01463
ingestedAt: '2026-09-08T15:33:26.990Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

mm/huge_memory: fix folio isn't locked in softleaf_to_folio()

On arm64 server, we found folio that get from migration entry isn't locked
in softleaf_to_folio().  This issue triggers when mTHP splitting and
zap_nonpresent_ptes() races, and the root cause is lack of memory barrier
in softleaf_to_folio().  The race is as follows:

	CPU0                                             CPU1

deferred_split_scan()                              zap_nonpresent_ptes()
  lock folio
  split_folio()
    unmap_folio()
      change ptes to migration entries
    __split_folio_to_order()                         softleaf_to_folio()
      set flags(including PG_locked) for tail pages    folio = pfn_folio(softleaf_to_pfn(entry))
      smp_wmb()                                        VM_WARN_ON_ONCE(!folio_test_locked(folio))
      prep_compound_page() for tail pages

In __split_folio_to_order(), smp_wmb() guarantees page flags of tail pages
are visible before the tail page becomes non-compound.  smp_wmb() should
be paired with smp_rmb() in softleaf_to_folio(), which is missed.  As a
result, if zap_nonpresent_ptes() accesses migration entry that stores tail
pfn, softleaf_to_folio() may see the updated compound_head of tail page
before page->flags.

This issue will trigger VM_WARN_ON_ONCE() in pfn_swap_entry_folio()
because of the race between folio split and zap_nonpresent_ptes()
leading to a folio incorrectly undergoing modification without a folio
lock being held.

This is a BUG_ON() before commit 93976a20345b ("mm: eliminate further
swapops predicates"), which in merged in v6.19-rc1.

To fix it, add missing smp_rmb() if the softleaf entry is migration entry
in softleaf_to_folio() and softleaf_to_page().

[tujinjiang@huawei.com: update function name and comments]

## Affected

- `Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b < 426ee10711586617da869c8bb798214965337617`
- `Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b < f1acf5887c2bbaf998dc3fe32c72b7a8b84a3ddd`
- `Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b < 722cfaf6b31d31123439e67b5deac6b1261a3dea`
- `Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b < 7ddcf4a245c1c5a91fdd9698757e3d95179ffe41`
- `Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b < b8c49ad888892ad7b77062b9c102b799a3e9b4f8`
- `Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b < 7ad1997b9bc8032603df8f091761114479285769`
- `Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b < 8bfb8414e9f2ce6f5f2f0e3d0da52f2d132128e7`
- `Linux >= e9b61f19858a5d6c42ce2298cf138279375d0d9b < 4c5e7f0fcd592801c9cc18f29f80fbee84eb8669`
- `Linux 4.5`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.