Stability issues with nested Hyper-V

[mmhx]

Hi there,

I've been digging quite a bit before I decided to write here.
I've been trying to get a Win 2022 Server with Hyper-V for nested VMs running (on PVE).

- I followed the docs for Nested Virtualization and created a machine with the Win11/2022 recommended settings
- I created a snapshot after each (imo) relevant change to easily hop back and try something else
- Installed Win2022 Server (en-US version, DE had some issues as I found out , just leaving this here if someone stumbles over it)
- I had to change machine back to pc-i440 to be able to boot with Hyper-V installed (otherwise it would be stuck on boot)

The status is that I can install Hyper-V and get a VM running, but after a some time (15 minutes to multiple hrs) the (Win 2022) VM will crash and be completely unresponsive. After it happens the first time it seems to happen faster the next time.

- I found mentions that Windows Updates make Hyper-V unstable, so I tried without installing (and delaying) updates -> no help
- I had a (migrated) Windows Server 2012 VM, that showed the exact same behaviour, so I figured it wasn't the 2022 Version
- After uninstalling Hyper-V again, the machine stays stable.

I found this reddit thread which seems to describe my issue rather well, but I also found mentions (in the docs history) that the svm flag is passed anyways, I tried to verify this within windows, but Windows did not show "Virtualization enabled" only "Virtual machine" ?
I booted the VM from a live linux, and /proc/cpuinfo showed the 'svm' flag

At this point I'm quite out of ideas. Pls help

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Some information about the system (not sure what would be important)

CPU(s) 64 x AMD EPYC 7313 16-Core Processor (2 Sockets)

Kernel Version Linux 5.13.19-2-pve #1 SMP PVE 5.13.19-4 (Mon, 29 Nov 2021 12:10:09 +0100)

PVE Manager Version pve-manager/7.1-8/5b267f33

 

[mmhx]

Strangest thing is... I set the present ( from ps -aux) cpu args along with +svm to test.... and its still running...
Nvm it just held out longer than usual.

But now it keeps crashing after just a few minutes. Something seems to change when it happens the first time (and it shoudnt have been Updates). I can pinpoint the time of failure in the event logs, but I cannot find anything suspicious in the 5 minutes before...

 

[mmhx]

Just as an update, I could not get this to work. So I uninstalled Hyper-V from this Win Server 2022 VM and set up Hyper-V Core on another VM, which runs smoothly.
I can use the 2022 VM to control the Hyper-V Core VM, but without proper domain environment (or at least with these VMs not being part of it) it's not smooth.