GPU-Passthrough of my iGPU into QEMU-KVM logs me out even though Optimus should be forcing the system to only use the discrete Nvidia card

My Thinkpad T470p has a discrete Geforce 940MX and integrated Intel HD 630. I am using Optimus Manager to have the default to boot with Nvidia, and I know this works because everything is twice as fast, and games will tell me they are using that GPU. The problem is, after all the config editing and initramfs generating steps needed to allow for GPU-Passthrough in QEMU-KVM through Virtual Machine Manager, it immediately logs me out as soon as I start installation of a VM with it selected in the PCI Host Device section, forcibly canceling the installation. Optimus logs me out when switching GPUs, of course, so this tells me the iGPU is still being used somewhere for some reason.

This makes even less sense to me because hybrid mode in Optimus would use the iGPU as the main, and send overflow to the discrete one, so it overall runs worse than when not just set to discrete, but nothing says anything about the iGPU still being used when the discrete one is set. All I can find online is that the iGPU is unused when the discrete is switched to being main.

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With a desktop system this is fairly manageable, but not always easily, With Optimus laptops, this is not so straight forward. Generally, Optimus does in fact co-opt the iGPU, as a passthrough for the dGPU and requires (quite a bit ) more work. If you are lucky enough to have an older iGPU that has GVT-d (pre 10th gen) you might possibly be able to set up a virtual gpu and accomplish what you want. Just so you know, most people are trying to share the dGPU, and not the iGPU as I believe you are stating.

In any event, I am sharing this link passthrough in hopes that it might if nothing else put you on the path to success for what you want to accomplish. At a minimum, it should resolve any confusion about muxless, mux’ed, and provide more insight into what you are experiencing.

Woah, that site is the most comprehensive post I’ve ever seen on this stuff. Thank you!
After reading it all, I think I may wait until I setup my Desktop PC instead of dealing with it on the laptop. I definitely have the MUXless scheme. But either way, you have made the quickest and most useful reply I’ve ever gotten on a Linux forum. Thank you again.

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