GPU Passthrough

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GPU Passthrough

Neil Sikka

Hello, I am trying to passthrough my ATI Radeon HD 8800M GPU to a Windows7 DomU from a Debian 7.11 Dom0 running kernel 3.19.1 with xen_pciback loaded as a module on xen-4.4.0 in a Dell Precision M4800 laptop with VT-d enabled and “nopat” and “pciback.hide” in grub. My setup is that I have the laptop connected via VGA to an external monitor and I can successfully see my desktop spread over the external monitor and the laptop screen.

Whether I have the fglrx driver loaded or am using software rendering, I still get the same behavior: I see the early hypervisor and kernel print statements to the console, and then it switches to X to correctly show the KDM login screen. The problem in both cases is that when I hit Ctrl+Alt+F1 to get back to any of the virtual terminals, the screen is black. This issue does not reproduce when I boot the same kernel directly without Xen. I'm thinking this could have to do with Kernel Mode Setting, but I'm not sure.

The reason I am debugging Ctrl+Alt+F1 showing a black screen is because I suspect that the VGA passthrough is working, but I cannot see the DomU output on the laptop screen because it stays black due to the same bug thats causing Ctrl+Alt+F1 to show a black screen. I am speculating that fixing the Ctrl+Alt+F1 blackscreen problem would also fix the DomU VGA passthrough problem. The reason I think the passthrough works is because the DomU boots up, and xl list shows the DomU running over ssh to Dom0.


Thanks in Advance.

--
Twitter: @neilsikka

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