drm/i915: Assert that the partial VMA fits within the object

When creating a partial VMA assert that it first fits with the parent
object, and that if it covers the whole of the parent a normal view was
created instead.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161223145804.6605-5-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_vma.c

@@ -95,8 +95,13 @@ __i915_vma_create(struct drm_i915_gem_object *obj,
 	if (view) {
 		vma->ggtt_view = *view;
 		if (view->type == I915_GGTT_VIEW_PARTIAL) {
+			GEM_BUG_ON(range_overflows_t(u64,
+						     view->params.partial.offset,
+						     view->params.partial.size,
+						     obj->base.size >> PAGE_SHIFT));
 			vma->size = view->params.partial.size;
 			vma->size <<= PAGE_SHIFT;
+			GEM_BUG_ON(vma->size >= obj->base.size);
 		} else if (view->type == I915_GGTT_VIEW_ROTATED) {
 			vma->size =
 				intel_rotation_info_size(&view->params.rotated);