Through bisecting, I found out that the commit http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=077fc1c04d70ef1748ac2daa6622b3320a1a004c causes a BSOD on my system when using vga passthrough with a AMD card (The usual 0x116 BSOD atikmdag.sys throws). Reverting this commit locally fixes this issue completely and reproducible, even with newer 4.5-versions of xen. Behaviour is reproducible with several 3.11+ kernels I tested (haven't tested <3.11 ones).

So it would be great if someone could review or revert this commit. I don't have any deeper knowledge about this commit or what it actually does, but would be happy to test possible fixes, so let me know if I can be of any help or should provide more information.