(In reply to Michel Dänzer from comment #3)
> FWIW, I don't think unbinding is supposed to be possible while Xorg (or
> anything else) is using the GPU. Sounds like there's something missing
> somewhere to prevent that.

Before I switched to AMD, I was passing an NVidia GPU (GTX 660) into my virtual
machine, and I could unbind and rebind it between nouveau and vfio-pci as much
as I wanted. No trouble at all. Even while X was running, once DRI3 support
came. I switched to AMD expecting the same functionality. Thankfully, not
having said functionality isn't the end of the world, but having to reboot my
computer every time I want to play a game in Windows right after playing a game
in Linux is exactly the kind of pain that I spent a summer setting up the VM to
avoid.