vhost-vdpa: fix backend feature ioctls

Commit 653055b9 ("vhost-vdpa: support get/set backend features")
introduces two malfunction backend features ioctls:

1) the ioctls was blindly added to vring ioctl instead of vdpa device
   ioctl
2) vhost_set_backend_features() was called when dev mutex has already
   been held which will lead a deadlock

This patch fixes the above issues.

Cc: Eli Cohen <elic@nvidia.com>
Reported-by: Zhu Lingshan <lingshan.zhu@intel.com>
Fixes: 653055b9 ("vhost-vdpa: support get/set backend features")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20200907104343.31141-1-jasowang@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vdpa.c

@@ -353,8 +353,6 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 	struct vdpa_callback cb;
 	struct vhost_virtqueue *vq;
 	struct vhost_vring_state s;
-	u64 __user *featurep = argp;
-	u64 features;
 	u32 idx;
 	long r;
 
@@ -381,18 +379,6 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 
 		vq->last_avail_idx = vq_state.avail_index;
 		break;
-	case VHOST_GET_BACKEND_FEATURES:
-		features = VHOST_VDPA_BACKEND_FEATURES;
-		if (copy_to_user(featurep, &features, sizeof(features)))
-			return -EFAULT;
-		return 0;
-	case VHOST_SET_BACKEND_FEATURES:
-		if (copy_from_user(&features, featurep, sizeof(features)))
-			return -EFAULT;
-		if (features & ~VHOST_VDPA_BACKEND_FEATURES)
-			return -EOPNOTSUPP;
-		vhost_set_backend_features(&v->vdev, features);
-		return 0;
 	}
 
 	r = vhost_vring_ioctl(&v->vdev, cmd, argp);
@@ -440,8 +426,20 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 	struct vhost_vdpa *v = filep->private_data;
 	struct vhost_dev *d = &v->vdev;
 	void __user *argp = (void __user *)arg;
+	u64 __user *featurep = argp;
+	u64 features;
 	long r;
 
+	if (cmd == VHOST_SET_BACKEND_FEATURES) {
+		r = copy_from_user(&features, featurep, sizeof(features));
+		if (r)
+			return r;
+		if (features & ~VHOST_VDPA_BACKEND_FEATURES)
+			return -EOPNOTSUPP;
+		vhost_set_backend_features(&v->vdev, features);
+		return 0;
+	}
+
 	mutex_lock(&d->mutex);
 
 	switch (cmd) {
@@ -476,6 +474,10 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 	case VHOST_VDPA_SET_CONFIG_CALL:
 		r = vhost_vdpa_set_config_call(v, argp);
 		break;
+	case VHOST_GET_BACKEND_FEATURES:
+		features = VHOST_VDPA_BACKEND_FEATURES;
+		r = copy_to_user(featurep, &features, sizeof(features));
+		break;
 	default:
 		r = vhost_dev_ioctl(&v->vdev, cmd, argp);
 		if (r == -ENOIOCTLCMD)