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

Summary

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.

Timeline

1. Sep 24, 2026, 3:10 PM UTCCVE published
2. Oct 19, 2026, 9:07 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 368076f52ebeecd33e10a9f80905d7508b6b6149 · fixed in 5c0d7b658cda62cd17cb3652783386d5608030ef; From 368076f52ebeecd33e10a9f80905d7508b6b6149 · fixed in d4b76d0b03cb49611312ecc4bcfb55ccdf0843e2

• Linux Linux

  6.19

• KernelLinux

  From 6.19.0 · fixed in 7.2.4

References 2