drm/i915: Stop holding a ref to the ppgtt from each vma

The context owns both the ppgtt and the vma within it, and our activity
tracking on the context ensures that we do not release active ppgtt. As
the context fulfils our obligations for active memory tracking, we can
relinquish the reference from the vma.

This fixes a silly transient refleak from closed vma being kept alive
until the entire system was idle, keeping all vm alive as well.
Reported-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Testcase: igt/gem_ctx_create/files
Fixes: 3365e226 ("drm/i915: Lazily unbind vma on close")
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@linux.intel.com>
Tested-by: NMika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180816073448.19396-1-chris@chris-wilson.co.uk
(cherry picked from commit a4417b7b)
Signed-off-by: NRodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/i915_vma.c

@@ -199,7 +199,6 @@ vma_create(struct drm_i915_gem_object *obj,
 		vma->flags |= I915_VMA_GGTT;
 		list_add(&vma->obj_link, &obj->vma_list);
 	} else {
-		i915_ppgtt_get(i915_vm_to_ppgtt(vm));
 		list_add_tail(&vma->obj_link, &obj->vma_list);
 	}
 
@@ -807,9 +806,6 @@ static void __i915_vma_destroy(struct i915_vma *vma)
 	if (vma->obj)
 		rb_erase(&vma->obj_node, &vma->obj->vma_tree);
 
-	if (!i915_vma_is_ggtt(vma))
-		i915_ppgtt_put(i915_vm_to_ppgtt(vma->vm));
-
 	rbtree_postorder_for_each_entry_safe(iter, n, &vma->active, node) {
 		GEM_BUG_ON(i915_gem_active_isset(&iter->base));
 		kfree(iter);