CVE-2026-64172: KVM: SVM: Disable AVIC IPI virtualization on Hygon Family 18h (erratum #1235)

From: Greg Kroah-Hartman <[email protected]>

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

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

KVM: SVM: Disable AVIC IPI virtualization on Hygon Family 18h (erratum #1235)

Hygon Family 18h CPUs are derived from AMD Family 17h (Zen1) silicon and
share the same erratum #1235: hardware may read a stale IsRunning=1 bit
during ICR write emulation and silently fail to generate an
AVIC_IPI_FAILURE_TARGET_NOT_RUNNING VM-Exit on the sending vCPU.

The absence of the VM-Exit causes KVM to miss the required wakeup of
blocking target vCPUs, leading to hung vCPUs and unbounded delays in
guest execution.

Extend the existing AMD Family 17h erratum #1235 workaround to also cover
Hygon Family 18h.  With IPI virtualization disabled, KVM never sets
IsRunning=1 in the Physical ID table, so every non-self IPI generates a
VM-Exit and is correctly emulated.

The Linux kernel CVE team has assigned CVE-2026-64172 to this issue.


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

	Issue introduced in 6.17 with commit 8de4a1c8164e5b2e40d1df764840a31de983f40b and fixed in 6.18.34 with commit 94ade38f317ea086a181db0e6b69c574b3b70a5e
	Issue introduced in 6.17 with commit 8de4a1c8164e5b2e40d1df764840a31de983f40b and fixed in 7.0.11 with commit 9560e6fee887a9594a89fa265b5b9c79b1591803
	Issue introduced in 6.17 with commit 8de4a1c8164e5b2e40d1df764840a31de983f40b and fixed in 7.1 with commit 9a12fa5213cfc391e0eed63902d3be98f0913765

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-2026-64172
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:
	arch/x86/kvm/svm/avic.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/94ade38f317ea086a181db0e6b69c574b3b70a5e
	https://git.kernel.org/stable/c/9560e6fee887a9594a89fa265b5b9c79b1591803
	https://git.kernel.org/stable/c/9a12fa5213cfc391e0eed63902d3be98f0913765