---
id: "CVE-2026-98715"
kind: "vulnerability"
aliases: ["CVE-2026-98715"]
title: "Linux KVM: failed VMRUN on AMD SVM drops a pending TLB flush"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["amd-svm", "hypervisor", "kvm", "linux", "runtime"]
not_affected_if: ["intel-only-hosts", "no-kvm"]
published_at: "2026-10-18T16:17:25+00:00"
first_seen_at: "2026-10-23T21:57:16+00:00"
updated_at: "2026-10-25T05:17:28+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98715", "first_seen_at": "2026-10-23T21:57:16+00:00"}]
---

# Linux KVM: failed VMRUN on AMD SVM drops a pending TLB flush

On AMD SVM hosts, KVM cleared the VMCB's TLB control after a failed VMRUN, which dropped a pending TLB flush the CPU would have performed on success. The sources describe a correctness flaw with possible noisy-neighbor effects rather than a confirmed code-execution path.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `uname -r` on KVM hosts and compare against the fixed kernel in the NVD entry (unknown in the sources)
- Check whether the host uses AMD CPUs with SVM: `grep -m1 svm /proc/cpuinfo`

## Fix

- Update the Linux kernel on KVM hosts to a release containing the upstream fix for CVE-2026-98715 (exact version unknown in the sources)

## Timeline

- 2026-10-23T21:57:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98715

## From the sources

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

KVM: SVM: Preserve TLB control (i.e. pending TLB flush) on failed VMRUN

Don't reset the VMCB's TLB control back to "do nothing" on a failed VMRUN,
as empirical testing shows that the CPU performs the requested TLB flush if
and only if VMRUN is successful, i.e. clearing TLB control on a failed
VMRUN effectively drops a TLB flush.

Explicitly track the need to flush all ASIDs on a per-CPU basis, as the
ASID reuse condition is tied to the pCPU, not to the vCPU.  As a bonus,
this also obviates the need to avoid clobbering FLUSH_ALL_ASID with
TLB_CONTROL_FLUSH_ASID, e.g. in svm_flush_tlb_asid().

Deliberately don't bother saving/restoring the "old" tlb_ctl on failure,
in quotes because it's not exactly the old tlb_ctl, it's the tlb_ctl from
after pre_svm_run(), but before updating tlb_ctl for flush_all_asids.  If
VMRUN fails and TLB_CONTROL_FLUSH_ALL_ASID is forced, then the next
successful run of the VMCB *may* unnecessarily flush all ASIDs, which
strictly speaking could result in noisy neighbor issues.  However, the
fact that new_asid() is already guest-triggerable, because of KVM's flawed
behavior of clearing the ASID on emulated INIT, means that a guest can
already trigger a flush of all ASIDs at roughly the same rate.  And once
KVM stops clobbering the ASID on emulated INIT, *or* assigns a static ASID
to each vCPU, this flaw goes away.

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