IOMMU Device Separation in to Groups

[Karel7]

I know this has been tackled already a couple of time but I have not seen any conclusions. My issue is that I have two graphics cards on a ASUS ROG Maximus X Hero motherboard w/i7-8700K CPU. I have enable IOMMU and all the other stuff, swapped cards around etc. The resulting groups I get are these. Passthrough just does not work and often hangs the VMs. Is this a dead end and I need a different motherboard?

Nvidia is 01:00
AMD is 04:00

/sys/kernel/iommu_groups/0/devices/0000:00:00.0
/sys/kernel/iommu_groups/1/devices/0000:00:01.0
/sys/kernel/iommu_groups/1/devices/0000:00:01.1
/sys/kernel/iommu_groups/1/devices/0000:01:00.0
/sys/kernel/iommu_groups/1/devices/0000:01:00.1
/sys/kernel/iommu_groups/1/devices/0000:01:00.2
/sys/kernel/iommu_groups/1/devices/0000:01:00.3
/sys/kernel/iommu_groups/1/devices/0000:02:00.0
/sys/kernel/iommu_groups/1/devices/0000:03:00.0
/sys/kernel/iommu_groups/1/devices/0000:04:00.0
/sys/kernel/iommu_groups/1/devices/0000:04:00.1
/sys/kernel/iommu_groups/2/devices/0000:00:14.0
/sys/kernel/iommu_groups/3/devices/0000:00:16.0
/sys/kernel/iommu_groups/4/devices/0000:00:17.0
/sys/kernel/iommu_groups/5/devices/0000:00:1b.0
/sys/kernel/iommu_groups/6/devices/0000:00:1c.0
/sys/kernel/iommu_groups/7/devices/0000:00:1c.2
/sys/kernel/iommu_groups/8/devices/0000:00:1c.4
/sys/kernel/iommu_groups/9/devices/0000:00:1c.6
/sys/kernel/iommu_groups/10/devices/0000:00:1d.0
/sys/kernel/iommu_groups/11/devices/0000:00:1f.0
/sys/kernel/iommu_groups/11/devices/0000:00:1f.2
/sys/kernel/iommu_groups/11/devices/0000:00:1f.3
/sys/kernel/iommu_groups/11/devices/0000:00:1f.4
/sys/kernel/iommu_groups/12/devices/0000:00:1f.6
/sys/kernel/iommu_groups/13/devices/0000:05:00.0
/sys/kernel/iommu_groups/14/devices/0000:07:00.0
/sys/kernel/iommu_groups/15/devices/0000:08:00.0
/sys/kernel/iommu_groups/16/devices/0000:09:00.0
/sys/kernel/iommu_groups/17/devices/0000:0a:00.0

 

[xi784]

adding "pcie_acs_override=downstream" to kernel boot commandline ?
or
pcie_acs_override=downstream,multifunction

 

[Karel7]

@xi784 Thank you! The multifunction did the trick. Never heard of the option before. Many thanks!

 

[LnxBil]

@xi784 Thank you! The multifunction did the trick. Never heard of the option before. Many thanks!

As far as I can see, both cards were - in addition to a lot of other stuff - in the same control group.