In following the guidelines on detaching PCI devices, making them available for VM passthrough I have done this for a GPU(Nvidia Quadro P2000) on a Dell PowerEdge R820 and a Nvidia GTX-970 on a Asrock Rack Xeon Server and in both cases, output was not correct. On the Dell, all my 3 monitors go active (wake up) and I have a mouse cursor that I can move from screen to screen in a Windows 10 vm. No icons or desktop ever appears. On the Asrock system I get absolutely no output at all. The monitors never wake up and it is as if the card is getting no signal.
I have confirmed that these VMs are working properly by using the VNC device to log in to them. I have removed VNC from both to see if somehow that intefered with the passthrough but I get the same results.
Another issue is that the detached devices are not persistant and do not survive reboots. This means that when we actually get the VMs to function with passthrough properly, after a reboot those VMs will not autostart as the PCI devices will not be available to them. I tagged this as MEDIUM as I believe this is a major function that must work. Reduce it to low if you disagree, Along with the GPU I have also passed through a USB 3.1 PCI card. Should not have any impact on the problem at hand.
I have a debug for your review, just could not find the private area to submit.
Let me know if you require anything else. Thank you.