xen-tools -- virtio: unbounded memory allocation issue

The Xen Project reports:

A guest can submit virtio requests without bothering to wait for
completion and is therefore not bound by virtqueue size…
A malicious guest administrator can cause unbounded memory
allocation in QEMU, which can cause an Out-of-Memory condition
in the domain running qemu. Thus, a malicious guest administrator
can cause a denial of service affecting the whole host.