CVE-2026-89915

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.