Xen HVM
========
Xen qemu-dm USB passthru using USB 1.1 emulation
Xen PVUSB support in Xen 4.0 (PVUSB drivers)(USB 2.0 and USB 1.1)
(dom0 kernel (xen-usbback) and the frontend driver (xen-usbfront) in the VM. )
USBIP

Xen PV
======
PVUSB
USBIP

Qemu-dm emulates USB 1.1 UHCI 2-port controller

/etc/xen/<guest> cfg

usb = 1
usbdevice = "host:xxxx:yyyy"