Slides are available for my talk at KVM Forum 2015 about virtio-vsock: Zero-configuration host/guest communication.
virtio-vsock is a new host/guest communications mechanism that allows applications to use the Sockets API to communicate between the hypervisor and virtual machines. It uses the AF_VSOCK address family which was introduced in Linux in 2013.
There are several advantages of virtio-serial. The main advantage is the familiar Sockets API semantics, which is more convenient than serial ports. See the slides for full details on what virtio-vsock offers.