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Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

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  Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs Joerg Roedel <jroedel@suse.de> - 2017-06-15 16:10 +0200
    Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs Samuel Sieb <samuel@sieb.net> - 2017-06-15 19:10 +0200
      RE: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs "Deucher, Alexander" <Alexander.Deucher@amd.com> - 2017-06-15 20:20 +0200
    Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs Bjorn Helgaas <helgaas@kernel.org> - 2017-06-15 21:20 +0200
      Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs Joerg Roedel <jroedel@suse.de> - 2017-06-16 18:30 +0200

#1666750 — Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

Hi Bjorn,

On Fri, Apr 07, 2017 at 04:32:18PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
> 
> ATS is broken on this hardware and causes IOMMU stalls and
> system failure. Disable ATS on these devices to make them
> usable again with IOMMU enabled.
> 
> Note that the commit in the Fixes-tag is not buggy, it
> just uncovers the problem in the hardware by increasing
> the ATS-flush rate.
> 
> Fixes: b1516a14657a ('iommu/amd: Implement flush queue')
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
>  drivers/pci/quirks.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)

Any more objections on this patch? Please let me know if you want to
have something changed.


Regards,

	Joerg

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#1666906

On 06/15/2017 07:04 AM, Joerg Roedel wrote:
> Hi Bjorn,
> 
> On Fri, Apr 07, 2017 at 04:32:18PM +0200, Joerg Roedel wrote:
>> From: Joerg Roedel <jroedel@suse.de>
>>
>> ATS is broken on this hardware and causes IOMMU stalls and
>> system failure. Disable ATS on these devices to make them
>> usable again with IOMMU enabled.
>>
>> Note that the commit in the Fixes-tag is not buggy, it
>> just uncovers the problem in the hardware by increasing
>> the ATS-flush rate.
>>
>> Fixes: b1516a14657a ('iommu/amd: Implement flush queue')
>> Signed-off-by: Joerg Roedel <jroedel@suse.de>
>> ---
>>   drivers/pci/quirks.c | 19 +++++++++++++++++++
>>   1 file changed, 19 insertions(+)
> 
> Any more objections on this patch? Please let me know if you want to
> have something changed.

The other patch seems to fix this issue without disabling ATS.  Isn't 
that better?

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#1667033

> -----Original Message-----
> From: Samuel Sieb [mailto:samuel@sieb.net]
> Sent: Thursday, June 15, 2017 1:02 PM
> To: Joerg Roedel; Bjorn Helgaas
> Cc: linux-pci@vger.kernel.org; linux-kernel@vger.kernel.org; Daniel Drake;
> Deucher, Alexander; David Woodhouse
> Subject: Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs
> 
> On 06/15/2017 07:04 AM, Joerg Roedel wrote:
> > Hi Bjorn,
> >
> > On Fri, Apr 07, 2017 at 04:32:18PM +0200, Joerg Roedel wrote:
> >> From: Joerg Roedel <jroedel@suse.de>
> >>
> >> ATS is broken on this hardware and causes IOMMU stalls and
> >> system failure. Disable ATS on these devices to make them
> >> usable again with IOMMU enabled.
> >>
> >> Note that the commit in the Fixes-tag is not buggy, it
> >> just uncovers the problem in the hardware by increasing
> >> the ATS-flush rate.
> >>
> >> Fixes: b1516a14657a ('iommu/amd: Implement flush queue')
> >> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> >> ---
> >>   drivers/pci/quirks.c | 19 +++++++++++++++++++
> >>   1 file changed, 19 insertions(+)
> >
> > Any more objections on this patch? Please let me know if you want to
> > have something changed.
> 
> The other patch seems to fix this issue without disabling ATS.  Isn't
> that better?

I talked to our validation team and ATS was validated on Stoney, so this patch is just working around something else.  The other patch fixes it and is a valid optimization (it should be applied eventually), but apparently the current behavior is allowed even if it's now optimal.  I'm not really an ATS expert.

Alex

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#1667191

On Thu, Jun 15, 2017 at 04:04:21PM +0200, Joerg Roedel wrote:
> Hi Bjorn,
> 
> On Fri, Apr 07, 2017 at 04:32:18PM +0200, Joerg Roedel wrote:
> > From: Joerg Roedel <jroedel@suse.de>
> > 
> > ATS is broken on this hardware and causes IOMMU stalls and
> > system failure. Disable ATS on these devices to make them
> > usable again with IOMMU enabled.
> > 
> > Note that the commit in the Fixes-tag is not buggy, it
> > just uncovers the problem in the hardware by increasing
> > the ATS-flush rate.
> > 
> > Fixes: b1516a14657a ('iommu/amd: Implement flush queue')
> > Signed-off-by: Joerg Roedel <jroedel@suse.de>
> > ---
> >  drivers/pci/quirks.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> 
> Any more objections on this patch? Please let me know if you want to
> have something changed.

It was marked "superseded" in patchwork and thus off my radar.  I
don't remember if I did that or why.  I changed it back to "New" so I
won't forget about it.

You mention (May 24) the original bug report.  Can you include the URL
for that?

I admit I just don't have warm fuzzies that the problem is well
understood.

Bjorn

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#1667876

Hi Bjorn,

On Thu, Jun 15, 2017 at 02:15:45PM -0500, Bjorn Helgaas wrote:
> It was marked "superseded" in patchwork and thus off my radar.  I
> don't remember if I did that or why.  I changed it back to "New" so I
> won't forget about it.

Great!

> You mention (May 24) the original bug report.  Can you include the URL
> for that?

I think there were multiple reports, here is one I could still find:

	https://lists.linuxfoundation.org/pipermail/iommu/2017-March/020836.html

> I admit I just don't have warm fuzzies that the problem is well
> understood.

The current understanding (without my ability to debug the hardware
involved) is that the GPU in the Stoney systems gets into a weird state
when ATS invalidations are sent too fast and stops responding to the
iommu.

The iommu then can't complete the invalidation commands and the driver
throws completion-wait loop timeout messages out.



	Joerg

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