drm/i915: inline vma_create into lookup_or_create_vma

In the execbuf code we don't clean up any vmas which ended up not
getting bound for code simplicity. To make sure that we don't end up
creating multiple vma for the same vm kill the somewhat dangerous
vma_create function and inline it into lookup_or_create.

This is just a safety measure to prevent surprises in the future.

Also update the somewhat confused comment in the execbuf code and
clarify what kind of magic is going on with a new one.

v2: Keep the function separate as requested by Chris. But give it a __
prefix for paranoia and move it tighter together with the other vma
stuff.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ben Widawsky <ben@bwidawsk.net>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1826,8 +1826,6 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
 struct drm_i915_gem_object *i915_gem_alloc_object(struct drm_device *dev,
 						  size_t size);
 void i915_gem_free_object(struct drm_gem_object *obj);
-struct i915_vma *i915_gem_vma_create(struct drm_i915_gem_object *obj,
-				     struct i915_address_space *vm);
 void i915_gem_vma_destroy(struct i915_vma *vma);
 
 int __must_check i915_gem_object_pin(struct drm_i915_gem_object *obj,

drivers/gpu/drm/i915/i915_gem.c

@@ -4109,8 +4109,19 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
 	i915_gem_object_free(obj);
 }
 
-struct i915_vma *i915_gem_vma_create(struct drm_i915_gem_object *obj,
+struct i915_vma *i915_gem_obj_to_vma(struct drm_i915_gem_object *obj,
 				     struct i915_address_space *vm)
+{
+	struct i915_vma *vma;
+	list_for_each_entry(vma, &obj->vma_list, vma_link)
+		if (vma->vm == vm)
+			return vma;
+
+	return NULL;
+}
+
+static struct i915_vma *__i915_gem_vma_create(struct drm_i915_gem_object *obj,
+					      struct i915_address_space *vm)
 {
 	struct i915_vma *vma = kzalloc(sizeof(*vma), GFP_KERNEL);
 	if (vma == NULL)
@@ -4131,6 +4142,19 @@ struct i915_vma *i915_gem_vma_create(struct drm_i915_gem_object *obj,
 	return vma;
 }
 
+struct i915_vma *
+i915_gem_obj_lookup_or_create_vma(struct drm_i915_gem_object *obj,
+				  struct i915_address_space *vm)
+{
+	struct i915_vma *vma;
+
+	vma = i915_gem_obj_to_vma(obj, vm);
+	if (!vma)
+		vma = __i915_gem_vma_create(obj, vm);
+
+	return vma;
+}
+
 void i915_gem_vma_destroy(struct i915_vma *vma)
 {
 	WARN_ON(vma->node.allocated);
@@ -4857,27 +4881,3 @@ unsigned long i915_gem_obj_size(struct drm_i915_gem_object *o,
 
 	return 0;
 }
-
-struct i915_vma *i915_gem_obj_to_vma(struct drm_i915_gem_object *obj,
-				     struct i915_address_space *vm)
-{
-	struct i915_vma *vma;
-	list_for_each_entry(vma, &obj->vma_list, vma_link)
-		if (vma->vm == vm)
-			return vma;
-
-	return NULL;
-}
-
-struct i915_vma *
-i915_gem_obj_lookup_or_create_vma(struct drm_i915_gem_object *obj,
-				  struct i915_address_space *vm)
-{
-	struct i915_vma *vma;
-
-	vma = i915_gem_obj_to_vma(obj, vm);
-	if (!vma)
-		vma = i915_gem_vma_create(obj, vm);
-
-	return vma;
-}

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -123,11 +123,16 @@ eb_lookup_vmas(struct eb_vmas *eb,
 	list_for_each_entry(obj, &objects, obj_exec_link) {
 		struct i915_vma *vma;
 
+		/*
+		 * NOTE: We can leak any vmas created here when something fails
+		 * later on. But that's no issue since vma_unbind can deal with
+		 * vmas which are not actually bound. And since only
+		 * lookup_or_create exists as an interface to get at the vma
+		 * from the (obj, vm) we don't run the risk of creating
+		 * duplicated vmas for the same vm.
+		 */
 		vma = i915_gem_obj_lookup_or_create_vma(obj, vm);
 		if (IS_ERR(vma)) {
-			/* XXX: We don't need an error path fro vma because if
-			 * the vma was created just for this execbuf, object
-			 * unreference should kill it off.*/
 			DRM_DEBUG("Failed to lookup VMA\n");
 			ret = PTR_ERR(vma);
 			goto out;

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -392,7 +392,7 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
 	if (gtt_offset == I915_GTT_OFFSET_NONE)
 		return obj;
 
-	vma = i915_gem_vma_create(obj, ggtt);
+	vma = i915_gem_obj_lookup_or_create_vma(obj, ggtt);
 	if (IS_ERR(vma)) {
 		ret = PTR_ERR(vma);
 		goto err_out;