args: -cpu host,-hypervisor No longer boot since Windows Update 01-2026 ( KB5073723 KB5073457 KB5074109 KB5073379 ) AMD EPYC 7302p

[_gabriel]

Seems I'm encountering a bug.
Host CPU is AMD 7302P
( EPYC Zen2 "Rome" ) on HPE DL325 G10.
PVE 8.4 ( Enterprise version 8.4.16 )
proxmox-ve: 8.4.0
running kernel: 6.8.12-18-pve
pve-manager: 8.4.16
pve-qemu-kvm: 9.2.0-7
qemu-server: 8.4.5

VM guest : Windows 10 ESU, 2019 , 2022 , 2025 , UEFI (No Secure boot ), SeaBIOS
works fine with args: -cpu host,-hypervisor
Once January 2026 Windows Update,
Windows no longer boots,
VM hangs before the spinning circle.
I haven't another AMD EPYC at the hand
and not reproducible with a Intel E-2346 on PVE 8.4

Anyone can test ?

 

[_gabriel]

Doesn't boot either with EPYC-Rome-v4,-hypervisor where EPYC-Rome-v4 alone works.
Works with args: -cpu EPYC,-hypervisor
Waiting the next month if Microsoft fixes the fix, like the Stop Code UNSUPPORTED_PROCESSOR BSOD.

 

[_gabriel]

Same after today Microsoft Windows Update.
args: -cpu EPYC,-hypervisor is required instead args: -cpu host,-hypervisor / args: -cpu: EPYC-Rome-v4,-hypervisor

 

[_gabriel]

-cpu host,-hypervisor,model=1 alternative boot ok post December 2025 Windows Update.
-cpu host,-hypervisor,model=1 forces EPYC 1th gen code name "Naples" but better cosmetic as real processor name displayed.
-cpu EPYC,-hypervisor model=49 forces EPYC 1th gen + override model to 2th gen code name "Rome" = No boot post December 2025 Windows Update.

 

[AntonJ]

PVE 9.15
AMD EPYC 9135

Windows Server 2025 OS Build 26100.32370 (February update), UEFI, no TPM
cpu: host,flags=-nested-virt boots and works with no problem.
cpu: EPYC,flags=-nested-virt boots and works but displays "AMD EPYC" as processor

Will be migrating win 2016,2019,2022 from VMware upcoming week, can do more tests then.

 

[uzumo]

Is viommu enabled? If so, why not disable it and try starting it?

*I recall that the issue only occurred when virtualization was enabled exclusively on Windows running on a virtual machine.

I recall it not starting when viommu was enabled. I don't know why it won't start.

If this doesn't concern you, I apologize.