On request from IRC, I also tried using UXA instead of SNA with the intel driver. It does not crash anymore, but when I try to enable the 2nd monitor, I get a "xrandr: Configure crtc 6 failed" and the following output in the Xorg.log: [ 1537.831] randr: falling back to unsynchronized pixmap sharing [ 1537.831] randr: failed to set shadow slave pixmap [ 1537.831] (EE) intel(G0): failed to set mode: No space left on device