drm/i915: Introduce GEM proxy

GEM proxy is a kind of GEM, whose backing physical memory is pinned
and produced by guest VM and is used by host as read only. With GEM
proxy, host is able to access guest physical memory through GEM object
interface. As GEM proxy is such a special kind of GEM, a new flag
I915_GEM_OBJECT_IS_PROXY is introduced to ban host from changing the
backing storage of GEM proxy.

v3:
- update "Reviewed-by". (Joonas)

v2:
- return -ENXIO when pin and map pages of GEM proxy to kernel space.
  (Chris)

Here are the histories of this patch in "Dma-buf support for Gvt-g"
patch-set:

v14:
- return -ENXIO when gem proxy object is banned by ioctl.
  (Chris) (Daniel)

v13:
- add comments to GEM proxy. (Chris)
- don't ban GEM proxy in i915_gem_sw_finish_ioctl. (Chris)
- check GEM proxy bar after finishing i915_gem_object_wait. (Chris)
- remove GEM proxy bar in i915_gem_madvise_ioctl.

v6:
- add gem proxy barrier in the following ioctls. (Chris)
  i915_gem_set_caching_ioctl
  i915_gem_set_domain_ioctl
  i915_gem_sw_finish_ioctl
  i915_gem_set_tiling_ioctl
  i915_gem_madvise_ioctl

Signed-off-by: Tina Zhang <[email protected]>
Reviewed-by: Joonas Lahtinen <[email protected]> #v1
Reviewed-by: Chris Wilson <[email protected]>
Cc: Daniel Vetter <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Chris Wilson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

drivers/gpu/drm/i915/i915_gem.c

@@ -1619,7 +1619,19 @@ i915_gem_set_domain_ioctl(struct drm_device *dev, void *data,
 	if (err)
 		goto out;
 
-	/* Flush and acquire obj->pages so that we are coherent through
+	/*
+	 * Proxy objects do not control access to the backing storage, ergo
+	 * they cannot be used as a means to manipulate the cache domain
+	 * tracking for that backing storage. The proxy object is always
+	 * considered to be outside of any cache domain.
+	 */
+	if (i915_gem_object_is_proxy(obj)) {
+		err = -ENXIO;
+		goto out;
+	}
+
+	/*
+	 * Flush and acquire obj->pages so that we are coherent through
 	 * direct access in memory with previous cached writes through
 	 * shmemfs and that our cache domain tracking remains valid.
 	 * For example, if the obj->filp was moved to swap without us
@@ -1675,6 +1687,11 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
 	if (!obj)
 		return -ENOENT;
 
+	/*
+	 * Proxy objects are barred from CPU access, so there is no
+	 * need to ban sw_finish as it is a nop.
+	 */
+
 	/* Pinned buffers may be scanout, so flush the cache */
 	i915_gem_object_flush_if_display(obj);
 	i915_gem_object_put(obj);
@@ -2669,7 +2686,8 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
 	void *ptr;
 	int ret;
 
-	GEM_BUG_ON(!i915_gem_object_has_struct_page(obj));
+	if (unlikely(!i915_gem_object_has_struct_page(obj)))
+		return ERR_PTR(-ENXIO);
 
 	ret = mutex_lock_interruptible(&obj->mm.lock);
 	if (ret)
@@ -3888,6 +3906,15 @@ int i915_gem_set_caching_ioctl(struct drm_device *dev, void *data,
 	if (!obj)
 		return -ENOENT;
 
+	/*
+	 * The caching mode of proxy object is handled by its generator, and
+	 * not allowed to be changed by userspace.
+	 */
+	if (i915_gem_object_is_proxy(obj)) {
+		ret = -ENXIO;
+		goto out;
+	}
+
 	if (obj->cache_level == level)
 		goto out;
 

drivers/gpu/drm/i915/i915_gem_object.h

@@ -53,8 +53,9 @@ struct i915_lut_handle {
 
 struct drm_i915_gem_object_ops {
 	unsigned int flags;
-#define I915_GEM_OBJECT_HAS_STRUCT_PAGE BIT(0)
-#define I915_GEM_OBJECT_IS_SHRINKABLE   BIT(1)
+#define I915_GEM_OBJECT_HAS_STRUCT_PAGE	BIT(0)
+#define I915_GEM_OBJECT_IS_SHRINKABLE	BIT(1)
+#define I915_GEM_OBJECT_IS_PROXY	BIT(2)
 
 	/* Interface between the GEM object and its backing storage.
 	 * get_pages() is called once prior to the use of the associated set
@@ -361,6 +362,12 @@ i915_gem_object_is_shrinkable(const struct drm_i915_gem_object *obj)
 	return obj->ops->flags & I915_GEM_OBJECT_IS_SHRINKABLE;
 }
 
+static inline bool
+i915_gem_object_is_proxy(const struct drm_i915_gem_object *obj)
+{
+	return obj->ops->flags & I915_GEM_OBJECT_IS_PROXY;
+}
+
 static inline bool
 i915_gem_object_is_active(const struct drm_i915_gem_object *obj)
 {

drivers/gpu/drm/i915/i915_gem_tiling.c

@@ -345,6 +345,15 @@ i915_gem_set_tiling_ioctl(struct drm_device *dev, void *data,
 	if (!obj)
 		return -ENOENT;
 
+	/*
+	 * The tiling mode of proxy objects is handled by its generator, and
+	 * not allowed to be changed by userspace.
+	 */
+	if (i915_gem_object_is_proxy(obj)) {
+		err = -ENXIO;
+		goto err;
+	}
+
 	if (!i915_tiling_ok(obj, args->tiling_mode, args->stride)) {
 		err = -EINVAL;
 		goto err;