CVE-2026-93217: mm/madvise: skip device-private PMDs in cold and pageout walks

CVE-2026-93217: mm/madvise: skip device-private PMDs in cold and pageout walks

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2026-93217 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.19 with commit 368076f52ebeecd33e10a9f80905d7508b6b6149 and fixed in 7.2.4 with commit 5c0d7b658cda62cd17cb3652783386d5608030ef
	Issue introduced in 6.19 with commit 368076f52ebeecd33e10a9f80905d7508b6b6149 and fixed in 7.3-rc1 with commit d4b76d0b03cb49611312ecc4bcfb55ccdf0843e2

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-93217
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	mm/madvise.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/5c0d7b658cda62cd17cb3652783386d5608030ef
	https://git.kernel.org/stable/c/d4b76d0b03cb49611312ecc4bcfb55ccdf0843e2