GPU passthrough on Arch: vfio binding works, but QEMU won't start

So I've been trying to set up GPU passthrough on Arch, but I've run into a wall. I followed these two guides, mostly the first one though: GPU Passthrough Revisited , Non-root GPU passthrough . I followed each step exactly, and everything worked. Then, when I got to the part where I had to start QEMU, it didn't work. I successfully bound my GPU to vfio, but now I'm stuck. Here's the output of lspci -nnk for my GPU: 01:00.0 3D controller : NVIDIA Corporation GM107M [GeForce GTX 950M] [10de:139a] (rev a2) Subsystem: ASUSTeK Computer Inc. Device [1043:178d] Kernel driver in use: vfio-pci Kernel modules: nouveau, nvidia_drm, nvidia But then when I try to start qemu, I get this output: Invalid MIT-MAGIC-COOKIE-1 keyUnable to init server: Could not connect: Connection refused QEMU 2.9.0 monitor - type 'help' for more information (qemu) gtk initialization failed The MIT-MAGIC-COOKIE can be fixed by setting the WINDOW variable, but I still can't start up QEMU. Any idea what I'm doing wrong?