Bug 2540181 (CVE-2026-93217)

Summary: CVE-2026-93217 kernel: mm/madvise: skip device-private PMDs in cold and pageout walks
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's memory management subsystem. A race condition can occur when an HMM-based Graphics Processing Unit (GPU) driver interacts with `madvise(MADV_COLD)` or `MADV_PAGEOUT` operations. This can lead to a kernel panic, effectively causing a Denial of Service (DoS) on the affected system.
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Cloudforms Team: --- Target Upstream Version:
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Description OSIDB Bzimport 2026-09-24 15:21:51 UTC 
In the Linux kernel, the following vulnerability has been resolved:

mm/madvise: skip device-private PMDs in cold and pageout walks

madvise_cold_or_pageout_pte_range() takes pmd_trans_huge_lock(), whose
pmd_is_huge() check returns true for a device-private PMD.  The subsequent
!pmd_present() branch has a VM_BUG_ON() asserting migration is the only
allowed non-present case; a device-private PMD trips it.

Skip device-private PMDs in that non-present branch and continue to
huge_unlock before calling pmd_folio().  Downgrade the check to
VM_WARN_ON_ONCE() so an unexpected PMD softleaf logs a warning rather than
panicking.  Drop the thp_migration_supported() guard: it expands to
IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_SOFTLEAF), and both
pmd_is_migration_entry() and pmd_is_device_private_entry() already return
false when that config is not selected, so the guard suppresses only the
case where the warning would already be silent.

Potential trigger: an HMM-based GPU driver races with
madvise(MADV_COLD)/MADV_PAGEOUT: pmd_trans_huge(*pmd) reads true, then
migrate_vma_pages() flips the PMD to a device-private entry before the PMD
lock is acquired.
Comment 1 Mauro Matteo Cascella 2026-09-25 10:06:10 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93217.mbox