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

[Ville Syrjälä]

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>"

We also probably want
Cc: stable at vger.kernel.org
Fixes: 0dc987b699ce ("drm/i915/display: Add smem fallback allocation for dpt")

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