CVE-2026-89915

/// Technical description

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

KVM: arm64: Remove VM-wide VNCR mapping counter

The global VNCR mapping counter is used to decide whether an L1

provided VNCR page is mapped in L0 on any CPU at the point of

dealing with a TLB invalidation. It is incremented when a mapping

is made in the fixmap, and decremented when unmapped.

As it turns out, this tracking has several flaws:

- we are trying to invalidate TLBs, and the mapping is only an

opportunistic consequence of the TLB. Checking this counter to

decide whether a TLB needs to be invalidated may result in missed

invalidations.

- an L1 vcpu invalidating its own TLB (a very likely case) will not

succeed in invalidating the VNCR pseudo TLB because that page is

not mapped in L0 at this stage.

Given that this tracking fails at delivering the minimum guarantees

that are required and is only a performance optimisation, remove it

completely.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References