drm/i915/ttm: audit remaining bo->resource

In the near future TTM will have NULL bo->resource when the object is
initially created, plus after calling into pipeline-gutting. Try to
handle the remaining cases. In practice NULL bo->resource should be
taken to mean swapped-out or purged object.

v2 (Andrzej):
  - Rather make i915_ttm_cpu_maps_iomem() return false with NULL
    resource.

References: 516198d3 ("drm/i915: audit bo->resource usage v3")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230130101230.25347-2-matthew.auld@intel.comReviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Acked-by: Christian König <ckoenig.leichtzumerken@gmail.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

@@ -472,7 +472,7 @@ static int i915_ttm_shrink(struct drm_i915_gem_object *obj, unsigned int flags)
 	struct ttm_placement place = {};
 	int ret;
 
-	if (!bo->ttm || bo->resource->mem_type != TTM_PL_SYSTEM)
+	if (!bo->ttm || i915_ttm_cpu_maps_iomem(bo->resource))
 		return 0;
 
 	GEM_BUG_ON(!i915_tt->is_shmem);
@@ -511,7 +511,13 @@ static void i915_ttm_delete_mem_notify(struct ttm_buffer_object *bo)
 {
 	struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
 
-	if (bo->resource && !i915_ttm_is_ghost_object(bo)) {
+	/*
+	 * This gets called twice by ttm, so long as we have a ttm resource or
+	 * ttm_tt then we can still safely call this. Due to pipeline-gutting,
+	 * we maybe have NULL bo->resource, but in that case we should always
+	 * have a ttm alive (like if the pages are swapped out).
+	 */
+	if ((bo->resource || bo->ttm) && !i915_ttm_is_ghost_object(bo)) {
 		__i915_gem_object_pages_fini(obj);
 		i915_ttm_free_cached_io_rsgt(obj);
 	}

drivers/gpu/drm/i915/gem/i915_gem_ttm.h

@@ -98,7 +98,7 @@ static inline bool i915_ttm_gtt_binds_lmem(struct ttm_resource *mem)
 static inline bool i915_ttm_cpu_maps_iomem(struct ttm_resource *mem)
 {
 	/* Once / if we support GGTT, this is also false for cached ttm_tts */
-	return mem->mem_type != I915_PL_SYSTEM;
+	return mem && mem->mem_type != I915_PL_SYSTEM;
 }
 
 bool i915_ttm_resource_mappable(struct ttm_resource *res);

drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c

@@ -711,6 +711,10 @@ int i915_gem_obj_copy_ttm(struct drm_i915_gem_object *dst,
 
 	assert_object_held(dst);
 	assert_object_held(src);
+
+	if (GEM_WARN_ON(!src_bo->resource || !dst_bo->resource))
+		return -EINVAL;
+
 	i915_deps_init(&deps, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);
 
 	ret = dma_resv_reserve_fences(src_bo->base.resv, 1);

drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c

@@ -53,7 +53,7 @@ static int i915_ttm_backup(struct i915_gem_apply_to_region *apply,
 	unsigned int flags;
 	int err = 0;
 
-	if (bo->resource->mem_type == I915_PL_SYSTEM || obj->ttm.backup)
+	if (!i915_ttm_cpu_maps_iomem(bo->resource) || obj->ttm.backup)
 		return 0;
 
 	if (pm_apply->allow_gpu && i915_gem_object_evictable(obj))
@@ -187,6 +187,9 @@ static int i915_ttm_restore(struct i915_gem_apply_to_region *apply,
 		return err;
 
 	/* Content may have been swapped. */
+	if (!backup_bo->resource)
+		err = ttm_bo_validate(backup_bo, i915_ttm_sys_placement(), &ctx);
+	if (!err)
 		err = ttm_tt_populate(backup_bo->bdev, backup_bo->ttm, &ctx);
 	if (!err) {
 		err = i915_gem_obj_copy_ttm(obj, backup, pm_apply->allow_gpu,