drm/i915/dpt: Treat the DPT BO as a framebuffer

Currently i915_gem_object_is_framebuffer() doesn't treat the
BO containing the framebuffer's DPT as a framebuffer itself.
This means eg. that the shrinker can evict the DPT BO while
leaving the actual FB BO bound, when the DPT is allocated
from regular shmem.

That causes an immediate oops during hibernate as we
try to rewrite the PTEs inside the already evicted
DPT obj.

TODO: presumably this might also be the reason for the
DPT related display faults under heavy memory pressure,
but I'm still not sure how that would happen as the object
should be pinned by intel_dpt_pin() while in active use by
the display engine...

Cc: stable@vger.kernel.org
Cc: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Fixes: 0dc987b6 ("drm/i915/display: Add smem fallback allocation for dpt")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230320090522.9909-2-ville.syrjala@linux.intel.comReviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>

drivers/gpu/drm/i915/display/intel_dpt.c

@@ -301,6 +301,7 @@ intel_dpt_create(struct intel_framebuffer *fb)
 	vm->pte_encode = gen8_ggtt_pte_encode;
 
 	dpt->obj = dpt_obj;
+	dpt->obj->is_dpt = true;
 
 	return &dpt->vm;
 }
@@ -309,5 +310,6 @@ void intel_dpt_destroy(struct i915_address_space *vm)
 {
 	struct i915_dpt *dpt = i915_vm_to_dpt(vm);
 
+	dpt->obj->is_dpt = false;
 	i915_vm_put(&dpt->vm);
 }

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -303,7 +303,7 @@ i915_gem_object_never_mmap(const struct drm_i915_gem_object *obj)
 static inline bool
 i915_gem_object_is_framebuffer(const struct drm_i915_gem_object *obj)
 {
-	return READ_ONCE(obj->frontbuffer);
+	return READ_ONCE(obj->frontbuffer) || obj->is_dpt;
 }
 
 static inline unsigned int

drivers/gpu/drm/i915/gem/i915_gem_object_types.h

@@ -491,6 +491,9 @@ struct drm_i915_gem_object {
 	 */
 	unsigned int cache_dirty:1;
 
+	/* @is_dpt: Object houses a display page table (DPT) */
+	unsigned int is_dpt:1;
+
 	/**
 	 * @read_domains: Read memory domains.
 	 *