Windows VMs boot failure with UNSUPPORTED_PROCESSOR

Solution Verified - Updated

Environment

  • OpenShift Virtualization
  • Microsoft Windows Server 2025
  • Microsoft Windows 11 Desktop
  • AMD CPU

Issue

  • After June 2025 Windows Updates, a Windows Server 2025 VM and Windows 11 Desktop VM running on OpenShift Virtualization fails to boot with a Blue Screen STOP error noting an UNSUPPORTED_PROCESSOR exception code.

Resolution

  • The issue is resolved by applying Microsoft update KB5060829, please update.

  • It was first fixed by Microsoft in Content from blogs.windows.com is not included.Build 26120-4452

  • If updating is not possible, a workaround consists of modifying the Virtual Machine definition to enable it booting again. However the specific change needed may affect performance, so the recommendation is to use the workaround below to boot the VM once and remove/rollback Microsoft Updates. Then shutdown the VM again, revert the workaround and boot the VM, keeping those Microsoft Updates absent until further notice, so there are no performance issues.

  • Modify VM YAML specification to disable arch-capabilities in the CPU stanza as follows, then stop and start the VM:
<snip>
spec:
  template:
    spec:
      domain:
        cpu:
          features:
            - name: arch-capabilities
              policy: disable
<snip>
  • An alternate option is to set the CPU model to EPYC.

Root Cause

  • Microsoft Windows Issue

Diagnostic Steps

  • Check Windows VM console for boot error messages indicating UNSUPPORTED_PROCESSOR recurring.
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