Comment # 9 on bug 100399 from jimijames.bove@gmail.com

(In reply to Michel Dänzer from comment #8)
> Make sure nothing else (e.g. gdm in Wayland mode) is using the GPU you're
> trying to unbind either. Something like
> 
>  sudo lsof /dev/dri/*
> 
> shows which process is using which GPU device(s).

I did that way back when I first discovered this bug. I'll do it again just to
make sure when I'm back with the computer that has the virtual machine and AMD
GPU in a couple weeks.