virtio/s390: handle failures of READ_VQ_CONF ccw

In virtio_ccw_read_vq_conf() the return value of ccw_io_helper()
was not checked.
If the configuration could not be read properly, we'd wrongly assume a
queue size of 0.

Let's propagate any I/O error to virtio_ccw_setup_vq() so it may
properly fail.
Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/s390/virtio/virtio_ccw.c

@@ -400,12 +400,16 @@ static bool virtio_ccw_kvm_notify(struct virtqueue *vq)
 static int virtio_ccw_read_vq_conf(struct virtio_ccw_device *vcdev,
 				   struct ccw1 *ccw, int index)
 {
+	int ret;
+
 	vcdev->config_block->index = index;
 	ccw->cmd_code = CCW_CMD_READ_VQ_CONF;
 	ccw->flags = 0;
 	ccw->count = sizeof(struct vq_config_block);
 	ccw->cda = (__u32)(unsigned long)(vcdev->config_block);
-	ccw_io_helper(vcdev, ccw, VIRTIO_CCW_DOING_READ_VQ_CONF);
+	ret = ccw_io_helper(vcdev, ccw, VIRTIO_CCW_DOING_READ_VQ_CONF);
+	if (ret)
+		return ret;
 	return vcdev->config_block->num;
 }
 
@@ -503,6 +507,10 @@ static struct virtqueue *virtio_ccw_setup_vq(struct virtio_device *vdev,
 		goto out_err;
 	}
 	info->num = virtio_ccw_read_vq_conf(vcdev, ccw, i);
+	if (info->num < 0) {
+		err = info->num;
+		goto out_err;
+	}
 	size = PAGE_ALIGN(vring_size(info->num, KVM_VIRTIO_CCW_RING_ALIGN));
 	info->queue = alloc_pages_exact(size, GFP_KERNEL | __GFP_ZERO);
 	if (info->queue == NULL) {