Re: [PATCH] drm/i915/dpt: Make DPT object unshrinkable

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, May 23, 2024 at 09:25:45AM +0100, Tvrtko Ursulin wrote:
> 
> On 22/05/2024 16:29, Vidya Srinivas wrote:
> > In some scenarios, the DPT object gets shrunk but
> > the actual framebuffer did not and thus its still
> > there on the DPT's vm->bound_list. Then it tries to
> > rewrite the PTEs via a stale CPU mapping. This causes panic.
> > 
> > Suggested-by: Ville Syrjala <ville.syrjala@linux.intel.com>
> > Cc: stable@vger.kernel.org
> > Fixes: 0dc987b699ce ("drm/i915/display: Add smem fallback allocation for dpt")
> > Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
> > ---
> >   drivers/gpu/drm/i915/gem/i915_gem_object.h | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > index 3560a062d287..e6b485fc54d4 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > @@ -284,7 +284,8 @@ bool i915_gem_object_has_iomem(const struct drm_i915_gem_object *obj);
> >   static inline bool
> >   i915_gem_object_is_shrinkable(const struct drm_i915_gem_object *obj)
> >   {
> > -	return i915_gem_object_type_has(obj, I915_GEM_OBJECT_IS_SHRINKABLE);
> > +	return i915_gem_object_type_has(obj, I915_GEM_OBJECT_IS_SHRINKABLE) &&
> > +		!obj->is_dpt;
> 
> Is there a reason i915_gem_object_make_unshrinkable() cannot be used to 
> mark the object at a suitable place?

Do you have a suitable place in mind?
i915_gem_object_make_unshrinkable() contains some magic
ingredients so doesn't look like it can be called willy
nilly.

Anyways, looks like I forgot to reply that I already pushed this
with this extra comment added:
/* TODO: make DPT shrinkable when it has no bound vmas */

-- 
Ville Syrjälä
Intel