AMD : BSOD unsupported processor since Windows build 26100.4202+ ( update kb5060842 + its preview kb5058499 )

[KciNicK]

After repeatedly rebooting due to an "unsupported processor error," you can start the computer by performing "Startup Repair" in the recovery console that is started. (The computer will transition to Windows setup.)
KB5063060 (or KB5060842) will cause an installation error, but it will not be reinstalled.

In the recovery screen, you will need to install the virtio driver from the command prompt.

drvload D:\vioscsi\w11\amd64\vioscsi.inf

well, of course not installing the update will fix the problem, the thing is, those are cumulative updates, that means, no more updates

 

[masato]

The following settings resolved the "Unsupported Processor" issue:

args: -cpu 'host,arch_capabilities=off'

The following flags seem to be set when the CPU is host.
They were not present when using EPYC-v4 or physical installation.

 

[Nick Kooij]

The following settings resolved the "Unsupported Processor" issue:

args: -cpu 'host,arch_capabilities=off'

The following flags seem to be set when the CPU is host.
They were not present when using EPYC-v4 or physical installation.

Nice. That worked for me too.

Although I'm using the following custom cpu model rather than the args parameter:

cpu-model: host-fix
    flags -arch-capabilities
    reported-model host

 

[_gabriel]

args: -cpu 'host,arch_capabilities=off'

Thanks, works here.

 

[Manu11837]

Hi, I enountered the same issue (UNSUPPORTED_PROCESSOR BSOD) with a Windows Server 2025 VM (not via Proxmox, but via german hoster Netcup that uses KVM-based virtual machines) after installing KB5060842 (Build 26100.4349). The host uses a AMD EPYC 7702P CPU.

Unfortunately I can't change the CPU type as a customer, and enabling "Virtual Machine Platform" didn't help in my case (as Netcup doesn't provide nested virtualization). However, I was able to work-around the bluescreen by reducing the CPU cores from 4 to 1 in the server control panel, after which Windows was able to boot successfully (but with reduced performance as only 1 CPU core is usable - as soon as I increase the CPU cores to 2 or more, the BSOD occurs again).