[vfio-users] GPU Pass-through for Linux guest

[Zir Blazer]

If I recall correctly, doing VGA Passthrough in Linux presented different issues that those that you're used to in Windows. The major difference was that Windows and the Video Card Drivers doesn't mind if you do something like attaching a 2014 PCI Express Video Card directly to the 1996 440FX PCI Host Bridge, a configuration that is physically impossible, but that in virtualized enviroments works in a miracleously way simply because PCI and PCIe are compatible at the protocol level.Either the Linux Kernel or the Video Card Drivers do more sanity checks and will refuse to work when it figures that your topology is wrong. I think that it was possible to get VGA Passthrough working in Linux for as long as you respected the basics, which should be that you have a PCI Express Root Complex (Provided by the Q35 Chipset, the 440FX provides only a PCI Host Bridge, and not sure if there are Reverse Bridges for proper PCI Express support) that provides a PCIe Root Port (Device ioh3420) for the Video Card to be "slotted" into.
On QEMU command line, it would look like this:
-machine pc-q35-2.5,accel=kvm-device ioh3420,chassis=1,bus=pcie.0,id=pcie.1-device vfio-pci,multifunction=true,bus=pcie.1,addr=00.0,host=01:00.0-device vfio-pci,bus=pcie.1,addr=00.1,host=01:00.1 		 	   		  
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