[Intel-gfx] [PATCH] drm/i915: Guard against i915_ggtt_disable_guc() being invoked unconditionally

[Chris Wilson]

On Wed, May 31, 2017 at 06:01:10PM -0700, Michel Thierry wrote:
> On 5/31/2017 12:05 PM, Chris Wilson wrote:
> >Commit 7c3f86b6dc51 ("drm/i915: Invalidate the guc ggtt TLB upon
> >insertion") added the restoration of the invalidation routine after the
> >GuC was disabled, but missed that the GuC was unconditionally disabled
> >when not used. This then overwrites the invalidate routine for the older
> >chipsets, causing havoc and breaking resume as the most obvious victim.
> >
> >We place the guard inside i915_ggtt_disable_guc() to be backport
> >friendly (the bug was introduced into v4.11) but it would be preferred
> >to be in more control over when this was guard (i.e. do not try and
> >teardown the data structures before we have enabled them). That should
> >be true with the reorganisation of the guc loaders.
> >
> >Reported-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >Fixes: 7c3f86b6dc51 ("drm/i915: Invalidate the guc ggtt TLB upon insertion")
> >Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> >Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> >Cc: Oscar Mateo <oscar.mateo at intel.com>
> >Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> >Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
> >Cc: Arkadiusz Hiler <arkadiusz.hiler at intel.com>
> >Cc: <stable at vger.kernel.org> # v4.11+

> Reviewed-by: Michel Thierry <michel.thierry at intel.com>
> 
> btw the bug can only happen in 4.11; in 4.12+ this safeguard is
> already redundant since enable_guc_loading should be zero and
> ggtt_disable_guc is never called.

Thanks for the review, pushed so we can get it back to where it needs to
go. I'll send a patch to convert this to an assert in a moment.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre