[Bug 109366] NULL pointer at pcie_capability_read_dword with Radeon SI vfio passthrough

[Bug 109366] NULL pointer at pcie_capability_read_dword with Radeon SI vfio passthrough

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=109366

            Bug ID: 109366
           Summary: NULL pointer at pcie_capability_read_dword with Radeon
                    SI vfio passthrough
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: ryandbair@gmail.com

Created attachment 143131
  --> https://bugs.freedesktop.org/attachment.cgi?id=143131&action=edit
dmesg output

My guest is seeing the attached bug and call trace during boot. Kernel
4.20.2-200, also an issue on 4.19 series. 4.18 is similar with the older drm_
prefixed version of the function.

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[Bug 109366] NULL pointer at pcie_capability_read_dword with Radeon SI vfio passthrough

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https://bugs.freedesktop.org/show_bug.cgi?id=109366

--- Comment #1 from Alex Williamson <alex.williamson@redhat.com> ---
Use a Q35 VM configuration with the assigned GPU downstream of an emulated PCIe
root port as a workaround.  The driver assumes this configuration, presumably
it's the only one that exists on bare metal, and reads from the upstream device
without checking that it is actually present.

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[Bug 109366] NULL pointer at pcie_capability_read_dword with Radeon SI vfio passthrough

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=109366

Alex Deucher <alexdeucher@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|DRM/AMDgpu                  |DRM/Radeon

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[Bug 109366] NULL pointer at pcie_capability_read_dword with Radeon SI vfio passthrough

[bugzilla-daemon]

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https://bugs.freedesktop.org/show_bug.cgi?id=109366

--- Comment #2 from Alex Deucher <alexdeucher@gmail.com> ---
Created attachment 143133
  --> https://bugs.freedesktop.org/attachment.cgi?id=143133&action=edit
possible fix

Does this patch fix it?  dGPUs are always add in cards, so they always plug
into an upstream port on bare metal.  The driver needs to query the upstream
port to determine what pcie gen speeds and lanes are available on the platform
so that the driver can properly adjust them at runtime to save power.

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[Bug 109366] NULL pointer at pcie_capability_read_dword with Radeon SI vfio passthrough

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https://bugs.freedesktop.org/show_bug.cgi?id=109366

--- Comment #3 from Ryan Bair <ryandbair@gmail.com> ---
Thank you both for the responses. 

I can confirm using the Q35 machine type does not see this issue. 

I'm rebuilding a kernel today to test the patch and will report back.

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[Bug 109366] NULL pointer at pcie_capability_read_dword with Radeon SI vfio passthrough

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https://bugs.freedesktop.org/show_bug.cgi?id=109366

--- Comment #4 from Ryan Bair <ryandbair@gmail.com> ---
I can confirm the attached patch does fix the issue for i440FX.

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[Bug 109366] NULL pointer at pcie_capability_read_dword with Radeon SI vfio passthrough

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https://bugs.freedesktop.org/show_bug.cgi?id=109366

Martin Peres <martin.peres@free.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |MOVED

--- Comment #5 from Martin Peres <martin.peres@free.fr> ---
-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been
closed from further activity.

You can subscribe and participate further through the new bug through this link
to our GitLab instance: https://gitlab.freedesktop.org/drm/amd/issues/861.

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