drm/gem: Warn on illegal use of the dumb buffer interface v2

It happens on occasion that developers of generic user-space applications
abuse the dumb buffer API to get hold of drm buffers that they can both
mmap() and use for GPU acceleration, using the assumptions that dumb buffers
and buffers available for GPU are
a) The same type and can be aribtrarily type-casted.
b) fully coherent.

This patch makes the most widely used drivers warn nicely when that happens,
the next step will be to fail.

v2: Move drmP.h changes to drm_gem.h. Fix Radeon dumb mmap breakage.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 23 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 3e0cabe9b544..50b842231c26 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -346,6 +346,7 @@ static int
 i915_gem_create(struct drm_file *file,
 		struct drm_device *dev,
 		uint64_t size,
+		bool dumb,
 		uint32_t *handle_p)
 {
 	struct drm_i915_gem_object *obj;
@@ -361,6 +362,7 @@ i915_gem_create(struct drm_file *file,
 	if (obj == NULL)
 		return -ENOMEM;
 
+	obj->base.dumb = dumb;
 	ret = drm_gem_handle_create(file, &obj->base, &handle);
 	/* drop reference from allocate - handle holds it now */
 	drm_gem_object_unreference_unlocked(&obj->base);
@@ -380,7 +382,7 @@ i915_gem_dumb_create(struct drm_file *file,
 	args->pitch = ALIGN(args->width * DIV_ROUND_UP(args->bpp, 8), 64);
 	args->size = args->pitch * args->height;
 	return i915_gem_create(file, dev,
-			       args->size, &args->handle);
+			       args->size, true, &args->handle);
 }
 
 /**
@@ -393,7 +395,7 @@ i915_gem_create_ioctl(struct drm_device *dev, void *data,
 	struct drm_i915_gem_create *args = data;
 
 	return i915_gem_create(file, dev,
-			       args->size, &args->handle);
+			       args->size, false, &args->handle);
 }
 
 static inline int
@@ -1773,10 +1775,10 @@ static void i915_gem_object_free_mmap_offset(struct drm_i915_gem_object *obj)
 	drm_gem_free_mmap_offset(&obj->base);
 }
 
-int
+static int
 i915_gem_mmap_gtt(struct drm_file *file,
 		  struct drm_device *dev,
-		  uint32_t handle,
+		  uint32_t handle, bool dumb,
 		  uint64_t *offset)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -1793,6 +1795,13 @@ i915_gem_mmap_gtt(struct drm_file *file,
 		goto unlock;
 	}
 
+	/*
+	 * We don't allow dumb mmaps on objects created using another
+	 * interface.
+	 */
+	WARN_ONCE(dumb && !(obj->base.dumb || obj->base.import_attach),
+		  "Illegal dumb map of accelerated buffer.\n");
+
 	if (obj->base.size > dev_priv->gtt.mappable_end) {
 		ret = -E2BIG;
 		goto out;
@@ -1817,6 +1826,15 @@ unlock:
 	return ret;
 }
 
+int
+i915_gem_dumb_map_offset(struct drm_file *file,
+			 struct drm_device *dev,
+			 uint32_t handle,
+			 uint64_t *offset)
+{
+	return i915_gem_mmap_gtt(file, dev, handle, true, offset);
+}
+
 /**
  * i915_gem_mmap_gtt_ioctl - prepare an object for GTT mmap'ing
  * @dev: DRM device
@@ -1838,7 +1856,7 @@ i915_gem_mmap_gtt_ioctl(struct drm_device *dev, void *data,
 {
 	struct drm_i915_gem_mmap_gtt *args = data;
 
-	return i915_gem_mmap_gtt(file, dev, args->handle, &args->offset);
+	return i915_gem_mmap_gtt(file, dev, args->handle, false, &args->offset);
 }
 
 static inline int