I have 2 Nvidia GPUs. A 1070 and a 670. I was using both in two Windows 10 machines without issue.
A few days ago I decided I wanted to try Windows 11 and change some things regarding how my VMs and their disks were configured. So I updated Unraid to the lates Release Candidate. I also updated my motherboard BIOS because it was old and went through every setting in the BIOS to make sure everything was fine.

Now passthrough of my 670 doesn't work no matter what I do. Using OVMF the VM boots but the GPU presents the code 43 error, which is normal, but using SeaBIOS the VM doesn't do anything. Complete black screen with one core stuck at 100%. And I guess Windows never even boots because the router doesn't assign any IP to the VM. This is both in Windows 10 and 11. So my previous VM doesn't work any longer. The 1070 works fine.

The vBIOS of the 1070 supports UEFI but the vBIOS of the 670 does not. Because of that my Windows 10 VMs were OVMF for the 1070 and SeaBios for the 670.

I've noticed my Unraid boots in UEFI mode. I honestly don't know how it was before. But I wonder if Unraid being in UEFI doesn't play nicely with using SeaBIOS. Could that be what stops me from using my 670? In case it is, is there something I should be wary about if I were to disable the UEFI mode of Unraid to boot in Legacy mode?

Booting unraid in uefi mode should not be an issue to run non uefi gpu with seabios. It may depend on the gpu itself (?). But you say that in the past it worked, so...

If you want to try, I see that some uefi bioses for the gtx 670 are available in internet; without flashing the card, you can try and pass that bios to the vm and try ovmf.

You could also dump your own vbios (preferred) and add support for uefi gop, with a windows tool called GOP Updater.

Your gpu is gk104 (gpu architecture=4):

 

 

Your modified vbios will be in the same folder of the tool

 

Edited February 11, 20224 yr by ghost82