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

[Chris Wilson]

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 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.

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")

are missing from v5.10.15
-Chris