Hi, I tried to do GPU passthrough today. Did everything as described in @wendell's post. Well, I didn't blacklist the Radeon driver, but as I use a AMD GPU as my Linux GPU, I thought if I did this Arch wouldn't give me any video output (correct me if I'm wrong on this one).
Then I proceeded to create a VM with virt-manager and installed Win10 over the VNC, which worked great, then I passed through my RX480 and nothing happened. As I tried to turn my VM off again my PC crashed. If you need any log files, just tell me how I get them and I will post them.
newest Arch-Linux x64 with systemd bootloader
CPU: AMD FX-6100
RAM:some 16GB Corsair Kit (2*8GB)
Mobo: Asrock 990fx Killer Fatal1ty
Linux GPU: R9 270X
Guest GPU: RX 480