So just to shed some light on this AMD nested virtualization issues:
TLDR: pve5.15 - HyperV and Sandbox tested on Windows VM WORKING -- BUT SAME VM, GPU passthrough and i get the "unimplemented wrmsr error"
Configuration:
- amd ryzen 5950x
- asus x570 wifi gaming ii
Started with pve5.13, I have a primary windows VM with GPU passthrough. I wanted to run hyperV (WSL and sandbox) on it.
- I started with the CPU=default (KVM64), but cant enable hyperV.
- changed to CPU=host, got into windows, enabled CPU. restarted, hung on boot... no luck
- upgraded pve to 5.15
- Got the unimplemented wrmsr issue.
NEW windows VM saga:
- created NEW windows VM (no gpu passthrough), set CPU to host, and enabled hyperV and tested with sandbox... it works... note, i was using the pve console to interact with this new windows VM
- shutdown new windows VM, added my GPU... and ran into the unimplemented wrmsr issue.
- removed GPU, new windows VM booted and sandbox was working
Back to the old windows VM:
- removed the GPU, (hyperV enables, CPU=host still) -> using console, windows vm boots and sandbox works
- added GPU back... windows doesnt boot... black screen with cursor
- revert back to pve5.13 (same setup as original), GPU windows works, but no hyperV/Sandbox
Overall, I think that what is causing this sort of issue is actually gpu passthrough. Note GPU passthrough works flawlessly without hyperV/nested virtualization.
Hopefully someone with more knowledge can put two and two together and figure this out for us, more than happy to provide whatever info you need.