linux-kernel - Re: [REGRESSION] Too-low frequency limit for AMD GPU PCI-passed-through to Windows VM

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Date:   Mon, 24 Jan 2022 18:58:10 -0500
From:   James Turner <linuxkernel.foss@...rc-none.turner.link>
To:     "Lazar, Lijo" <Lijo.Lazar@....com>
Cc:     Alex Deucher <alexdeucher@...il.com>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Koenig, Christian" <Christian.Koenig@....com>
Subject: Re: [REGRESSION] Too-low frequency limit for AMD GPU
 PCI-passed-through to Windows VM

Hi Lijo,

> Not able to relate to how it affects gfx/mem DPM alone. Unless Alex
> has other ideas, would you be able to enable drm debug messages and
> share the log?

Sure, I'm happy to provide drm debug messages. Enabling everything
(0x1ff) generates *a lot* of log messages, though. Is there a smaller
subset that would be useful? Fwiw, I don't see much in the full drm logs
about the AMD GPU anyway; it's mostly about the Intel GPU.

All the messages in the system log containing "01:00" or "1002:6981" are
identical between the two versions.

I've posted below the only places in the logs which contain "amd". The
commit with the issue (f9b7f3703ff9) has a few drm log messages from
amdgpu which are not present in the logs for f1688bd69ec4.

# f1688bd69ec4 ("drm/amd/amdgpu:save psp ring wptr to avoid attack")

[drm] amdgpu kernel modesetting enabled.
vga_switcheroo: detected switching method \_SB_.PCI0.GFX0.ATPX handle
ATPX version 1, functions 0x00000033
amdgpu: CRAT table not found
amdgpu: Virtual CRAT table created for CPU
amdgpu: Topology: Add CPU node

# f9b7f3703ff9 ("drm/amdgpu/acpi: make ATPX/ATCS structures global (v2)")

[drm] amdgpu kernel modesetting enabled.
vga_switcheroo: detected switching method \_SB_.PCI0.GFX0.ATPX handle
ATPX version 1, functions 0x00000033
[drm:amdgpu_atif_pci_probe_handle.isra.0 [amdgpu]] Found ATIF handle \_SB_.PCI0.GFX0.ATIF
[drm:amdgpu_atif_pci_probe_handle.isra.0 [amdgpu]] ATIF version 1
[drm:amdgpu_acpi_detect [amdgpu]] SYSTEM_PARAMS: mask = 0x6, flags = 0x7
[drm:amdgpu_acpi_detect [amdgpu]] Notification enabled, command code = 0xd9
amdgpu: CRAT table not found
amdgpu: Virtual CRAT table created for CPU
amdgpu: Topology: Add CPU node

Other things I'm willing to try if they'd be useful:

- I could update to the 21.Q4 Radeon Pro driver in the Windows VM. (The
  21.Q3 driver is currently installed.)

- I could set up a Linux guest VM with PCI passthrough to compare to the
  Windows VM and obtain more debugging information.

- I could build a kernel with a patch applied, e.g. to disable some of
  the changes in f9b7f3703ff9.

James