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

From: Paul Menzel <pmenzel@molgen.mpg.de>
To: Thorsten Leemhuis <regressions@leemhuis.info>,
	James Turner <linuxkernel.foss@dmarc-none.turner.link>
Cc: "Xinhui Pan" <Xinhui.Pan@amd.com>,
	regressions@lists.linux.dev, kvm@vger.kernel.org,
	"Greg KH" <gregkh@linuxfoundation.org>,
	"Lijo Lazar" <lijo.lazar@amd.com>,
	LKML <linux-kernel@vger.kernel.org>,
	amd-gfx@lists.freedesktop.org,
	"Alexander Deucher" <Alexander.Deucher@amd.com>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Alex Deucher" <alexdeucher@gmail.com>,
	"Christian König" <Christian.Koenig@amd.com>
Subject: Re: [REGRESSION] Too-low frequency limit for AMD GPU PCI-passed-through to Windows VM
Date: Fri, 18 Mar 2022 06:43:10 +0100	[thread overview]
Message-ID: <40b3084a-11b8-0962-4b33-34b56d3a87a3@molgen.mpg.de> (raw)
In-Reply-To: <d541b534-8b83-b566-56eb-ea8baa7c998e@leemhuis.info>

Dear Thorsten, dear James,

Am 17.03.22 um 13:54 schrieb Thorsten Leemhuis:
> On 13.03.22 19:33, James Turner wrote:
>>
>>> My understanding at this point is that the root problem is probably
>>> not in the Linux kernel but rather something else (e.g. the machine
>>> firmware or AMD Windows driver) and that the change in f9b7f3703ff9
>>> ("drm/amdgpu/acpi: make ATPX/ATCS structures global (v2)") simply
>>> exposed the underlying problem.
> 
> FWIW: that in the end is irrelevant when it comes to the Linux kernel's
> 'no regressions' rule. For details see:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/admin-guide/reporting-regressions.rst
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/process/handling-regressions.rst
> 
> That being said: sometimes for the greater good it's better to not
> insist on that. And I guess that might be the case here.

But who decides that? Running stuff in a virtual machine is not that 
uncommon.

Should the commit be reverted, and re-added with a more elaborate commit 
message documenting the downsides?

Could the user be notified somehow? Can PCI passthrough and a loaded 
amdgpu driver be detected, so Linux warns about this?

Also, should this be documented in the code?

>> I'm not sure where to go from here. This issue isn't much of a concern
>> for me anymore, since blacklisting `amdgpu` works for my machine. At
>> this point, my understanding is that the root problem needs to be fixed
>> in AMD's Windows GPU driver or Dell's firmware, not the Linux kernel. If
>> any of the AMD developers on this thread would like to forward it to the
>> AMD Windows driver team, I'd be happy to work with AMD to fix the issue
>> properly.

(Thorsten, your mailer mangled the quote somehow – I reformatted it –, 
which is too bad, as this message is shown when clicking on the link 
*marked invalid* in the regzbot Web page [1]. (The link is a very nice 
feature.)

> In that case I'll drop it from the list of regressions, unless what I
> wrote above makes you change your mind.
> 
> #regzbot invalid: firmware issue exposed by kernel change, user seems to
> be happy with a workaround
> 
> Thx everyone who participated in handling this.

Should the regression issue be re-opened until the questions above are 
answered, and a more user friendly solution is found?

Kind regards,

Paul

[1]: https://linux-regtracking.leemhuis.info/regzbot/resolved/