drm/i915: avoid leaking DMA mappings

We have 3 types of DMA mappings for GEM objects:
1. physically contiguous for stolen and for objects needing contiguous
   memory
2. DMA-buf mappings imported via a DMA-buf attach operation
3. SG DMA mappings for shmem backed and userptr objects

For 1. and 2. the lifetime of the DMA mapping matches the lifetime of the
corresponding backing pages and so in practice we create/release the
mapping in the object's get_pages/put_pages callback.

For 3. the lifetime of the mapping matches that of any existing GPU binding
of the object, so we'll create the mapping when the object is bound to
the first vma and release the mapping when the object is unbound from its
last vma.

Since the object can be bound to multiple vmas, we can end up creating a
new DMA mapping in the 3. case even if the object already had one. This
is not allowed by the DMA API and can lead to leaked mapping data and
IOMMU memory space starvation in certain cases. For example HW IOMMU
drivers (intel_iommu) allocate a new range from their memory space
whenever a mapping is created, silently overriding a pre-existing
mapping.

Fix this by moving the creation/removal of DMA mappings to the object's
get_pages/put_pages callbacks. These callbacks already check for and do
an early return in case of any nested calls. This way objects of the 3.
case also become more like the other object types.

I noticed this issue by enabling DMA debugging, which got disabled after
a while due to its internal mapping tables getting full. It also reported
errors in connection to random other drivers that did a DMA mapping for
an address that was previously mapped by i915 but was never released.
Besides these diagnostic messages and the memory space starvation
problem for IOMMUs, I'm not aware of this causing a real issue.

The fix is based on a patch from Chris.

v2:
- move the DMA mapping create/remove calls to the get_pages/put_pages
  callbacks instead of adding new callbacks for these (Chris)
v3:
- also fix the get_page cache logic on the userptr async path (Chris)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -2139,6 +2139,8 @@ i915_gem_object_put_pages_gtt(struct drm_i915_gem_object *obj)
 		obj->base.read_domains = obj->base.write_domain = I915_GEM_DOMAIN_CPU;
 	}
 
+	i915_gem_gtt_finish_object(obj);
+
 	if (i915_gem_object_needs_bit17_swizzle(obj))
 		i915_gem_object_save_bit_17_swizzle(obj);
 
@@ -2199,6 +2201,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 	struct sg_page_iter sg_iter;
 	struct page *page;
 	unsigned long last_pfn = 0;	/* suppress gcc warning */
+	int ret;
 	gfp_t gfp;
 
 	/* Assert that the object is not currently in any GPU domain. As it
@@ -2246,8 +2249,10 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 			 */
 			i915_gem_shrink_all(dev_priv);
 			page = shmem_read_mapping_page(mapping, i);
-			if (IS_ERR(page))
+			if (IS_ERR(page)) {
+				ret = PTR_ERR(page);
 				goto err_pages;
+			}
 		}
 #ifdef CONFIG_SWIOTLB
 		if (swiotlb_nr_tbl()) {
@@ -2276,6 +2281,10 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 		sg_mark_end(sg);
 	obj->pages = st;
 
+	ret = i915_gem_gtt_prepare_object(obj);
+	if (ret)
+		goto err_pages;
+
 	if (i915_gem_object_needs_bit17_swizzle(obj))
 		i915_gem_object_do_bit_17_swizzle(obj);
 
@@ -2300,10 +2309,10 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 	 * space and so want to translate the error from shmemfs back to our
 	 * usual understanding of ENOMEM.
 	 */
-	if (PTR_ERR(page) == -ENOSPC)
-		return -ENOMEM;
-	else
-		return PTR_ERR(page);
+	if (ret == -ENOSPC)
+		ret = -ENOMEM;
+
+	return ret;
 }
 
 /* Ensure that the associated pages are gathered from the backing storage
@@ -3248,10 +3257,8 @@ int i915_vma_unbind(struct i915_vma *vma)
 
 	/* Since the unbound list is global, only move to that list if
 	 * no more VMAs exist. */
-	if (list_empty(&obj->vma_list)) {
-		i915_gem_gtt_finish_object(obj);
+	if (list_empty(&obj->vma_list))
 		list_move_tail(&obj->global_list, &dev_priv->mm.unbound_list);
-	}
 
 	/* And finally now the object is completely decoupled from this vma,
 	 * we can drop its hold on the backing storage and allow it to be
@@ -3769,22 +3776,16 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj,
 		goto err_remove_node;
 	}
 
-	ret = i915_gem_gtt_prepare_object(obj);
-	if (ret)
-		goto err_remove_node;
-
 	trace_i915_vma_bind(vma, flags);
 	ret = i915_vma_bind(vma, obj->cache_level, flags);
 	if (ret)
-		goto err_finish_gtt;
+		goto err_remove_node;
 
 	list_move_tail(&obj->global_list, &dev_priv->mm.bound_list);
 	list_add_tail(&vma->mm_list, &vm->inactive_list);
 
 	return vma;
 
-err_finish_gtt:
-	i915_gem_gtt_finish_object(obj);
 err_remove_node:
 	drm_mm_remove_node(&vma->node);
 err_free_vma:

drivers/gpu/drm/i915/i915_gem_userptr.c

@@ -545,6 +545,26 @@ st_set_pages(struct sg_table **st, struct page **pvec, int num_pages)
 	return ret;
 }
 
+static int
+__i915_gem_userptr_set_pages(struct drm_i915_gem_object *obj,
+			     struct page **pvec, int num_pages)
+{
+	int ret;
+
+	ret = st_set_pages(&obj->pages, pvec, num_pages);
+	if (ret)
+		return ret;
+
+	ret = i915_gem_gtt_prepare_object(obj);
+	if (ret) {
+		sg_free_table(obj->pages);
+		kfree(obj->pages);
+		obj->pages = NULL;
+	}
+
+	return ret;
+}
+
 static void
 __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
 {
@@ -584,9 +604,12 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
 	if (obj->userptr.work != &work->work) {
 		ret = 0;
 	} else if (pinned == num_pages) {
-		ret = st_set_pages(&obj->pages, pvec, num_pages);
+		ret = __i915_gem_userptr_set_pages(obj, pvec, num_pages);
 		if (ret == 0) {
 			list_add_tail(&obj->global_list, &to_i915(dev)->mm.unbound_list);
+			obj->get_page.sg = obj->pages->sgl;
+			obj->get_page.last = 0;
+
 			pinned = 0;
 		}
 	}
@@ -693,7 +716,7 @@ i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
 			}
 		}
 	} else {
-		ret = st_set_pages(&obj->pages, pvec, num_pages);
+		ret = __i915_gem_userptr_set_pages(obj, pvec, num_pages);
 		if (ret == 0) {
 			obj->userptr.work = NULL;
 			pinned = 0;
@@ -715,6 +738,8 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj)
 	if (obj->madv != I915_MADV_WILLNEED)
 		obj->dirty = 0;
 
+	i915_gem_gtt_finish_object(obj);
+
 	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
 		struct page *page = sg_page_iter_page(&sg_iter);