How to apply a kernel patch? VFIO

I'm having issues with GPU pass-through. When I start the VM, host displays go black and VM display remains black as well. My issue matches question 4 on that page.
I can't figure out how to apply or find the patch mentioned in that answer (other VGA arbiter patch). And btw I'm trying to pass-through GPU2. My final goal is to pass-through the 280x, but currently if I do that, Cinnamon will start in fallback mode.

I followed this guide.

My setup:
Distro: Linux Mint 17.2 Cinnamon 64bit
Kernel: 3.19.0-30-generic
MB: Asus M5A97 pro
CPU: FX-8350
GPU1: AMD R280x
GPU2: ATI 4350/4550