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

[Srinivas, Vidya]

> -----Original Message-----
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Sent: Monday, May 20, 2024 10:10 PM
> To: Srinivas, Vidya <vidya.srinivas at intel.com>
> Cc: intel-gfx at lists.freedesktop.org; Syrjala, Ville <ville.syrjala at intel.com>; Lee,
> Shawn C <shawn.c.lee at intel.com>; Srinivas at freedesktop.org
> Subject: Re: [PATCH] drm/i915/dpt: Make DPT object unshrinkable
> 
> On Mon, May 20, 2024 at 08:54:10PM +0530, Srinivas, Vidya 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.
> >
> > Credits-to: Ville Syrjala <ville.syrjala at linux.intel.com>
> > 	    Shawn Lee <shawn.c.lee at intel.com>
> >
> > Signed-off-by: Srinivas, Vidya <vidya.srinivas at intel.com>
> 
> The format should be "first_name last_name <email>"

Apologies for the mistake. My gitconfig got messed up.

> 
> We also probably want
> Cc: stable at vger.kernel.org
> Fixes: 0dc987b699ce ("drm/i915/display: Add smem fallback allocation for
> dpt")
> 
Thank you so much. Will float new patch with this added.

> Although the patch won't actually build unless we also have commit
> 779cb5ba64ec ("drm/i915/dpt: Treat the DPT BO as a framebuffer") but that
> hast the same fixes tag, so should be fine even if someone backports things
> that far back.
> 
> > ---
> >  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)
> > {
> 
> Maybe toss something like this here:
> /* TODO: make DPT shrinkable when it has no bound vmas */
> 
> DPTs aren't necessarily so small that shrinking them wouldn't have any
> benefits. But actually implementing that would require some actual work, so
> not suitable for a quick fix.
> 
> I can add all that stuff when applying the patch, no need to resend for this.
> 
> > -	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;
> >  }
> >
> >  static inline bool
> > --
> > 2.34.1
> 
> --
> Ville Syrjälä
> Intel