---
id: CVE-2026-68093
title: >-
  KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after
  hotplug
summary: >-
  In the Linux kernel, the following vulnerability has been resolved:


  KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after
  hotplug


  If a vCPU stays scheduled out (or blocked) while the last pCPU it ran

  on goes throug…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb <
    2028b81321dc757b6875b99c10d908e349c141e2
  - >-
    Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb <
    60283726f2845bd78b95efbd0e50b93944780477
  - >-
    Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb <
    7508916b4b55d6f5ecc68cd09774dabd3a6b4440
  - >-
    Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb <
    0f33b1c457c2199ed130b92cc2ff363a3f7b9415
  - >-
    Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb <
    6b542d116acecb83a1ca34e8eace304cff6a4ec9
  - >-
    Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb <
    25f744ffa0c8e799e06250ce2e618367b166b0d4
  - Linux 2.6.21
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-06T16:42:24.942470Z'
published: '2026-08-10'
updated: '2026-11-06'
sourceUpdated: '2026-11-06T16:44:58.589Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-68093'
references:
  - url: 'https://git.kernel.org/stable/c/2028b81321dc757b6875b99c10d908e349c141e2'
  - url: 'https://git.kernel.org/stable/c/60283726f2845bd78b95efbd0e50b93944780477'
  - url: 'https://git.kernel.org/stable/c/7508916b4b55d6f5ecc68cd09774dabd3a6b4440'
  - url: 'https://git.kernel.org/stable/c/0f33b1c457c2199ed130b92cc2ff363a3f7b9415'
  - url: 'https://git.kernel.org/stable/c/6b542d116acecb83a1ca34e8eace304cff6a4ec9'
  - url: 'https://git.kernel.org/stable/c/25f744ffa0c8e799e06250ce2e618367b166b0d4'
tags:
  - cve.org
epss: 0.00186
epssPercentile: 0.08224
ingestedAt: '2026-11-06T16:57:43.147Z'
---

## Overview

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

KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug

If a vCPU stays scheduled out (or blocked) while the last pCPU it ran
on goes through a hotplug cycle (online->offline->online), and the vCPU
then resumes execution on the same pCPU, then it is possible for it to
run with an ASID that has now been assigned to a different vCPU,
resulting in stale TLB translations being used.

svm_enable_virtualization_cpu() resets asid_generation to 1 and sets
next_asid to max_asid + 1 on every CPU online event, including hotplug
cycles.  Because next_asid starts beyond the pool boundary, the first
call to new_asid() after an online event always wraps the pool,
incrementing asid_generation to 2 and assigning ASIDs starting from
min_asid.

Consider two vCPUs from different VMs, vCPU-A pinned to CPU-X holding
asid_generation=2 and ASID=N from before the hotplug event:

  1. CPU-X goes offline and back online: asid_generation resets to 1,
     next_asid = max_asid + 1.

  2. One or more vCPUs migrate to CPU-X and call new_asid(), wrapping
     the pool and consuming ASIDs starting from min_asid.  Eventually
     vCPU-B from a different VM is assigned asid_generation=2, ASID=N
     — the same ASID that vCPU-A held before the hotplug.

  3. vCPU-A enters pre_svm_run() on CPU-X: current_vmcb->cpu is
     unchanged so the migration branch is skipped.  Its saved
     asid_generation=2 matches sd->asid_generation=2, so the generation
     check silently passes and vCPU-A continues running with ASID=N —
     the same ASID just freshly assigned to vCPU-B.

Both vCPUs from different VMs now run on CPU-X with the same ASID,
causing them to share NPT TLB entries and producing stale translations.

The collision manifests as a KVM internal error (Suberror: 1, emulation
failure).  The NPT page fault reports a faulting GPA far outside the
VM's physical memory range — a sign of stale TLB translations being
used.  KVM falls back to instruction emulation, which fails on
FPU/XSave instructions (XRSTOR, STMXCSR) that the emulator does not
implement.

Fix this by incrementing asid_generation instead of resetting it to 1
in svm_enable_virtualization_cpu().  On module load, asid_generation
starts at 0 (memset) and the increment produces 1, identical to the
old behaviour.  On subsequent hotplug cycles the generation advances
beyond any value a vCPU previously observed on this CPU, so the
generation check in pre_svm_run() reliably forces new_asid() on every
vCPU after every hotplug cycle.

## Affected

- `Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb < 2028b81321dc757b6875b99c10d908e349c141e2`
- `Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb < 60283726f2845bd78b95efbd0e50b93944780477`
- `Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb < 7508916b4b55d6f5ecc68cd09774dabd3a6b4440`
- `Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb < 0f33b1c457c2199ed130b92cc2ff363a3f7b9415`
- `Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb < 6b542d116acecb83a1ca34e8eace304cff6a4ec9`
- `Linux >= 774c47f1d78e373a6bd2964f4e278d1ce26c21cb < 25f744ffa0c8e799e06250ce2e618367b166b0d4`
- `Linux 2.6.21`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.