Protect vhost device iotlb by vhost_dev->mutex. Otherwise,
it might cause corruption of the list and interval tree in
struct vhost_iotlb if userspace sends the VHOST_IOTLB_MSG_V2
message concurrently.

Fixes: 4c8cf318("vhost: introduce vDPA-based backend")
Cc: stable@vger.kernel.org
Signed-off-by: NXie Yongji <xieyongji@bytedance.com>
Acked-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NStefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20210412095512.178-1-xieyongji@bytedance.comSigned-off-by: NMichael S. Tsirkin <mst@redhat.com>