[SOLVED] WSL2 issue on Windows 2025 VM - PVE with Kernel 7.0 + QEMU 11 (works with QEMU 10)

[mvdhoeven]

Hi all,

I’m running into an issue with WSL2 inside a Windows Server 2025 VM after upgrading to Linux Kernel 7.0 and QEMU 11, and I’m hoping someone else has seen this or can point me in the right direction.

Environment​

• Proxmox cluster with 2 nodes
  • Node 1: ASRockRack X470D4U + Ryzen 7 3700X
  • Node 2: ASRockRack X470D4U2T + Ryzen 9 5900X
• Shared VM migration between nodes is required
• Windows Server 2025 VM running WSL2 (Debian 13)

To allow live migration between these two CPUs, I’m using a custom CPU profile with only flags supported by both processors

Working Setup​

• Kernel 7.0 + QEMU 10
  VM boots fine with custom CPU Profile
  WSL2 works and my Debian 13 installation executes (when starting the Debian 13 environment it does say wsl: Nested virtualization is not supported on this machine)
  Live migration between nodes works

Issue (after upgrading to QEMU 11)​

With the same custom CPU profile VM enters a boot loop and eventually lands in Windows Recovery

Behavior with different CPU types​

• Host CPU type
  Boots fine
  WSL2 works
  Cannot migrate (expected due to CPU mismatch)
• Default CPU type (x86-64-v3)
  Boots fine
  Migration works
  WSL2 does not work (WSL2 is unable to start as virtualization is not enabled for this machine)
• New Custom CPU type with the new suggested flags added
  Boots fine
  WSL2 does not work (WSL2 is unable to start as virtualization is not enabled for this machine

In short​

• QEMU 10 → everything works as expected
• QEMU 11 → WSL2 only works with host CPU profile, but that breaks migration
• Any attempt to combine migration-compatible CPU profile and nested virtualization leads to either bootloop (without the new suggested flags) or booting VM without WSL2 working (with level=30;-cet-ibt;-cet-ss flags)

Is there a recommended CPU profile that supports:

• migration between Zen 2 / Zen 3
• AND working virtualization for WSL2?

Thanks in advance!

 

[mvdhoeven]

Have been doing some more tests.
The key flag in the custom cpu profile is +svm as expected.
When that flag is removed from the custom cpu profile the VM boots, but will obviously break virtualization support.

Another thing I tried:
Reverted one node to QEMU 10.

Started the the Windows 2025 VM using the initial custom CPU profile on the QEMU 10 host.
As expected it booted and also Debian 13 WSL2 is running fine.
Exited the Debian instance and then I live migrated the VM to the other node that still has QEMU 11 installed.

Live migration was successful.
Started the WSL2 Debian instance again from Terminal and this is now also running on the QEMU 11 host.
Even the previous warning wsl: Nested virtualization is not supported on this machine is gone.

Restarting the VM on the QEMU 11 node then results in the boot loop again.

 

[fiona]

Hi,
please try using a virtual AMD CPU model close to your physical CPUs and enable the +nested-virt CPU flag.

 

[mvdhoeven]

Hi Fiona,

thanks for pushing me in the right direction. That solved it.
I was making it to complex by using a custom CPU model.
Now using EPYC as base CPU model. Then enabled all flags that were displayed as compatible for both nodes.

End result from qm config
cpu: EPYC,flags=+nested-virt;+aes;+amd-ssbd;+hv-tlbflush;+ibpb;+pdpe1gb;+ssbd;+virt-ssbd

Now the VM boots fine, WSL2 is working and the VM can be live migrated between the nodes.

Best regards,
Mathieu