[Bug 110571] GPU Passthrough of Vega 56 GPU hangs on KVM start.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110571

            Bug ID: 110571
           Summary: GPU Passthrough of Vega 56 GPU hangs on KVM start.
           Product: DRI
           Version: DRI git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: James.Dutton at gmail.com

When trying to use IOMMU and passthrough a Vega GPU to the guest VM.  KVM fails
to start, and SERR errors are shown with lspci on the GPU device.

Hardware is a Threadripper 1950X, Gigabyte X399 Pro motherboard.
Vega 56.

The same problem also happens with an old Radeon CAICOS GPU.

So, my theory is that this is a AMD Threadripper and X399 motherboard problem.
Maybe related to the IOMMU programming on the X399 chipset not happening
correctly.

Can anyone help give me some pointers as to where to look to help diagnose the
problem.
For example, how do I view iommu settings/mappings?
How do I find out what all the config params for the X399 Bridge GPP do?
What does GPP mean?

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