https://bugs.freedesktop.org/show_bug.cgi?id=100399
--- Comment #4 from jimijames.bove@gmail.com --- (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.