[vfio-users] (nested) WSL 2 under KVM

[Anthony M de Beus]

Host: manjaro, with the latest edk2-ovmf file from the Arch repos,
passing through a NVIDIA Quadro card.  The host is a Intel i7-4930K with
its own graphics card, a Radeon HD 7970.

Guest: I've been running Windows 10 Pro under KVM using libvirt for a
few years, currently was running version 1909, which runs WSL 1 without
issue. 

I updated to build 19041, which is necessary for WSL 2, which actually
runs a real linux kernel, AFAIK.  Updating worked OK, enabling WSL
worked OK, but running the VM enabling command (which is necessary for
WSL 2, but not WSL 1) under PowerShell:

dism.exe /online /enable-feature /featurename:VirtualMachinePlatform
/all /norestart

while working, causes the VM to hang at the OVMF boot screen at the next
reboot.  The "Performance" tab shows a constant 16%.

I have the following in my XML file

   <kvm>
      <hidden state='on'/>
    </kvm>
and
  <cpu mode='host-model' check='partial'>
    <topology sockets='1' cores='3' threads='2'/>
    <feature policy='disable' name='hypervisor'/>
  </cpu>

and Windows Powershell's Hyper-V requirements all say "yes" when typing
in "systeminfo" under cmd or powershell.  The hang is bad enough to
require reverting back to the previous Windows version (1909) and
starting all over again.  I also tried adding  <feature policy='require'
name='vmx'/> to the "cpu" section with the same result.

I presume the problem is that Windows VM nesting under KVM doesn't yet
work and that the issues are the same as for Hyper-V.  The latest thing
I found regarding nesting under KVM is
https://ladipro.wordpress.com/2017/07/21/hyperv-in-kvm-known-issues/
from 2017.   Anyone else tried this out? If there's a better place to
post this, please let me know.