https://bugs.freedesktop.org/show_bug.cgi?id=100399
--- Comment #9 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.