In the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Preserve TLB control (i.e. (CVE-2026-98715)

The Linux kernel vulnerability CVE-2026-98715 concerns the KVM SVM (Secure Virtual Machine) feature's handling of TLB (Translation Lookaside Buffer) control during failed VMRUN instructions. Previously, the VMCB's TLB control was reset to 'do nothing' on a failed VMRUN, but empirical testing showed that the CPU only performs the requested TLB flush if VMRUN succeeds. Resetting TLB control on failure caused the flush to be dropped, potentially leading to stale TLB entries. The fix preserves the TLB control state on failure and explicitly tracks the need to flush all ASIDs (Address Space Identifiers) on a per-CPU basis, aligning with the fact that ASID reuse is tied to physical CPUs, not virtual CPUs. This also simplifies the logic around TLB flush operations. While the fix may cause occasional unnecessary flushing of all ASIDs after a failed VMRUN, this is considered acceptable given existing guest-triggerable flushes and planned improvements in ASID handling.

The vulnerability could lead to dropped TLB flushes on failed VMRUN operations, potentially causing stale TLB entries to persist. This might result in noisy neighbor effects due to unnecessary flushing of all ASIDs on subsequent successful runs, which could degrade performance. However, the impact is limited to the internal handling of TLB flushes within the KVM SVM virtualization context and does not indicate direct security compromise or known exploitation. No known exploits in the wild have been reported.

The vulnerability has been resolved in the Linux kernel. Users should apply the official kernel updates that include this fix. Since this is a kernel-level fix, upgrading to the patched kernel version is the recommended remediation. No additional mitigation steps are indicated or required beyond applying the official fix.