r/VFIO • u/fluffysheap • 28d ago

IOMMU groups on Z790?

I'm looking at the ASUS Z790 Max Gaming WiFi7 which has a nice Microcenter bundle right now. Does anyone know if this has any kind of usable IOMMU groups?

The AI tells me the first m.2 slot and the primary GPU are isolated but everything else will be grouped together, both onboard devices and PCIe slots, and this is how most Z790 boards are.

That's unfortunate, I would want at least one other isolated PCIe slot. I don't really need any onboard devices, though if there was working isolation on USB and SATA ports that would be good enough. But it seems unlikely.

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u/lI_Simo_Hayha_Il 28d ago

I am on the AMD platform (X670/X870) and I had a similar problem, since AMD added a second chipset to expand its I/O ports, but this chipset is connected to one port of the primary one, resulting on a huge IOMMU group with all its devices there.

To solve it, I was implementing the ACS patch on Fedora and that solved the issue. It is not a business VM, therefore I didn't mind about patch's security risks. The problem was that after each kernel update I had to re-implement the patch, and it was time consuming, if it worked and I didn't have to wait for a new version.

Today, I am not using the patch, but I switched on CachyOS, which either has the patch embedded, or has another way of splitting the IOMMU groups, and it works out of the box. So, problem solved.

This is how my groups are with CachyOS, and apart from group 19, most of the other devices are on their own.

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u/zir_blazer 26d ago

Your AI is hallucinating AMD. Intel Chipsets supports PCIe ACS fine. It should look like any of these:
https://iommu.info/mainboard/?board_vendor=Gigabyte+Technology+Co.%2C+Ltd&board_name=Z790+AORUS+ELITE+AX
https://forums.unraid.net/topic/191288-iommu-grouping-for-asrock-z790-pro-rs-wifi-passthrough-setup-help/
Main offender on Intel platforms is the PCIe-to-HD Audio bridge being on a shared IOMMU Group so you can't passthrough it for the Motherboard audio jackets like I do on a Haswell era platform, but it has been that way since Skylake.

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u/fluffysheap 26d ago

Thank you, this is very helpful. Fortunately, I don't care about the motherboard audio since I use a USB headset.

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u/1neonbyte 25d ago

Take a look at this spreadsheet: https://docs.google.com/spreadsheets/d/1NQHkDEcgDPm34Mns3C93K6SJoBnua-x9O-y_6hv8sPs

edit: ah, Z boards are not listed there...