virtio-gpu: fix ioctl and expose the fixed status to userspace.

This exposes to mesa that it can use the fixed ioctl for querying
later cap sets, cap set 1 is forever frozen in time.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20180221015003.22884-1-airlied@gmail.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_ioctl.c

@@ -197,6 +197,9 @@ static int virtio_gpu_getparam_ioctl(struct drm_device *dev, void *data,
 	case VIRTGPU_PARAM_3D_FEATURES:
 		value = vgdev->has_virgl_3d == true ? 1 : 0;
 		break;
+	case VIRTGPU_PARAM_CAPSET_QUERY_FIX:
+		value = 1;
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -472,7 +475,7 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
 {
 	struct virtio_gpu_device *vgdev = dev->dev_private;
 	struct drm_virtgpu_get_caps *args = data;
-	int size;
+	unsigned size, host_caps_size;
 	int i;
 	int found_valid = -1;
 	int ret;
@@ -481,6 +484,10 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
 	if (vgdev->num_capsets == 0)
 		return -ENOSYS;
 
+	/* don't allow userspace to pass 0 */
+	if (args->size == 0)
+		return -EINVAL;
+
 	spin_lock(&vgdev->display_info_lock);
 	for (i = 0; i < vgdev->num_capsets; i++) {
 		if (vgdev->capsets[i].id == args->cap_set_id) {
@@ -496,11 +503,9 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
 		return -EINVAL;
 	}
 
-	size = vgdev->capsets[found_valid].max_size;
-	if (args->size > size) {
-		spin_unlock(&vgdev->display_info_lock);
-		return -EINVAL;
-	}
+	host_caps_size = vgdev->capsets[found_valid].max_size;
+	/* only copy to user the minimum of the host caps size or the guest caps size */
+	size = min(args->size, host_caps_size);
 
 	list_for_each_entry(cache_ent, &vgdev->cap_cache, head) {
 		if (cache_ent->id == args->cap_set_id &&

include/uapi/drm/virtgpu_drm.h

@@ -63,6 +63,7 @@ struct drm_virtgpu_execbuffer {
 };
 
 #define VIRTGPU_PARAM_3D_FEATURES 1 /* do we have 3D features in the hw */
+#define VIRTGPU_PARAM_CAPSET_QUERY_FIX 2 /* do we have the capset fix */
 
 struct drm_virtgpu_getparam {
 	__u64 param;