Hey There!

So I ended up updating my kernel to 5.17.0-11.1-liquorix so I could perform ACS Override for GPU Pass-through. ACS Override works but now my devices will not isolate and switch to the vfio-pci driver even though I have updated the boot code for it to do so. Any reason that this could be?

My cmdline looks like this:
GRUB_CMDLINE_LINUX_DEFAULT="amd_iommu=on iommu=pt kvm.ignore_msrs=1 vfio-pci.ids=10de:1b80,10de:10f0 pcie_acs_override=downstream,multifunction quiet splash"



lordsmeef
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This looks like a good question to ask the VFIO community at reddit.com/r/VFIO. From what I've read, getting everything to work well requires both the hardware and software to operate properly.

You mention you're using the ACS Override support. Overall what I understand is if your motherboard requires it, there's a high chance one part won't work anyways due to the lack of official support from the motherboard. You can read a previous thread from a few weeks ago regarding this same issue: techpatterns.com/forums/about2938.html

Although the thread was left open, the original author reached out in our Zen Kernel group chat and mentioned he fixed the issue through a BIOS update "and a little script for pci drivers" (verbatim last post).
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The only purpose ACS Override is being used for is to remap the IOMMU Group Numbers because some motherboards have a tendency to map the devices weird, official IOMMU Passthrough is still a supported feature on the Motherboard. It shouldn't change the behavior of the devices, just make it easier for the kernel to separate/isolate them. So the question still stands, why on a bone-stock kernel am I able to isolate, but with the current custom kernel, I can not isolate them. The device Id's are identical, the bus id's did not change, only that they have been separated in IOMMU Groups. Now I think the OP of the post you linked forgot to mention something, you are not able to isolate the devices in this custom version of the kernal EVEN if ACS Support is off. That's why I am suspicious that it is a software level issue. I will check over at VFIO and see what they have to say.

Thanks!
lordsmeef
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I have solved the issue.
After digging around some I found a guide here: https://mathiashueber.com/windows-virtual-machine-gpu-passthrough-ubuntu/

Ubuntu was on a older kernel version (5.15x) that would allow the isolation perimeter to work through the Grub config (vfio_pci-ids=) apperantly 5.17.0-11.1-liquorix does not allow you to do this.

For those with this issue, the guide above shows you how to properly isolate and divert your nvidia card from Nouveau/Nvidia to the vfio-pci driver. You have to pull some strings, but it is worth it in the end.

If your device mapping is weird, the acs override patch and perimeter(pcie_acs_override=downstream,multifunction) is still required to break up the devices and you will have to modify this in your grub cfg.

lordsmeef
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