Re: [Intel-gfx] [5.10.y regression] i915 clear-residuals mitigation is causing gfx issues

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 2/11/21 1:26 PM, Hans de Goede wrote:
> Hi,
> 
> On 2/11/21 11:49 AM, Chris Wilson wrote:
>> Quoting Hans de Goede (2021-02-11 10:36:13)
>>> Hi,
>>>
>>> On 2/10/21 1:48 PM, Chris Wilson wrote:
>>>> Quoting Hans de Goede (2021-02-10 10:37:19)
>>>>> Hi,
>>>>>
>>>>> On 2/10/21 12:07 AM, Chris Wilson wrote:
>>>>>> Quoting Hans de Goede (2021-02-09 11:46:46)
>>>>>>> Hi,
>>>>>>>
>>>>>>> On 2/9/21 12:27 AM, Chris Wilson wrote:
>>>>>>>> Quoting Hans de Goede (2021-02-08 20:38:58)
>>>>>>>>> Hi All,
>>>>>>>>>
>>>>>>>>> We (Fedora) have been receiving reports from multiple users about gfx issues / glitches
>>>>>>>>> stating with 5.10.9. All reporters are users of Ivy Bridge / Haswell iGPUs and all
>>>>>>>>> reporters report that adding i915.mitigations=off to the cmdline fixes things, see:
>>>>>>>>
>>>>>>>> I tried to reproduce this on the w/e on hsw-gt1, to no avail; and piglit
>>>>>>>> did not report any differences with and without mitigations. I have yet
>>>>>>>> to test other platforms. So I don't yet have an alternative.
>>>>>>>
>>>>>>> Note the original / first reporter of:
>>>>>>>
>>>>>>> https://bugzilla.redhat.com/show_bug.cgi?id=1925346
>>>>>>>
>>>>>>> Is using hsw-gt2, so it seems that the problem is not just the enabling of
>>>>>>> the mitigations on ivy-bridge / bay-trail but that there actually is
>>>>>>> a regression on devices where the WA worked fine before...
>>>>>>
>>>>>> There have been 3 crashes uploaded related to v5.10.9, and in all 3
>>>>>> cases the ACTHD has been in the first page. This strongly suggests that
>>>>>> the w/a is scribbling over address 0. And there's then a very good
>>>>>> chance that
>>>>>>
>>>>>> commit 29d35b73ead4e41aa0d1a954c9bfbdce659ec5d6
>>>>>> Author: Chris Wilson <chris@chris-wilson.co.uk>
>>>>>> Date:   Mon Jan 25 12:50:33 2021 +0000
>>>>>>
>>>>>>     drm/i915/gt: Always try to reserve GGTT address 0x0
>>>>>>     
>>>>>>     commit 489140b5ba2e7cc4b853c29e0591895ddb462a82 upstream.
>>>>>>
>>>>>> in v5.10.14 is sufficient to hide the issue.
>>>>>
>>>>> That one actually is already in v5.10.13 and the various reportes of these
>>>>> issues have already tested 5.10.13. They did mention that it took longer
>>>>> to reproduce with 5.10.13 then with 5.10.10, but that could also be due to:
>>>>>
>>>>> "drm/i915/gt: Clear CACHE_MODE prior to clearing residuals"
>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.10.y&id=520d05a77b2866eb4cb9e548e1d8c8abcfe60ec5
>>>>
>>>> Started looking for scratch page overwrites, and found this little gem:
>>>> https://patchwork.freedesktop.org/patch/420436/?series=86947&rev=1
>>>>
>>>> Looks promising wrt the cause of overwriting random addresses -- and
>>>> I hope that is the explanation for the glitches/hangs. I have a hsw gt2
>>>> with gnome shell, piglit is happy, but I suspect it is all due to
>>>> placement and so will only occur at random.
>>>
>>> If you can give me a list of commits to cherry-pick then I can prepare
>>> a Fedora 5.10.y kernel which those added for the group of Fedora users
>>> who are hitting this to test.
>>
>> e627d5923cae ("drm/i915/gt: One more flush for Baytrail clear residuals")
>> d30bbd62b1bf ("drm/i915/gt: Flush before changing register state")
>> 1914911f4aa0 ("drm/i915/gt: Correct surface base address for renderclear")
> 
> Thanks, the test-kernel is building now. I will let you know when I have
> heard back from the Fedora users (this will likely take 1-2 days).

I've heard back from 2 of the reporters who were seeing issues with 5.10.9+

And I'm happy to report 5.10.15 + the 3 commits mentioned above cherry-picked
on top fixes the graphics glitches for them.

So if we can get these 3 commits into 5.10.y and 5.11.y then this should be
resolved.

Regards,

Hans

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