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

[Hans de Goede]

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 at 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.

FWIW those users have reported back that the 3 reverts which I mentioned
earlier do indeed restore normal functionality (without glitches) for them.

Regards,

Hans