Description of problem:

KVM allows to passthrough USB devices to the virtual machine.
This is done with the --usbdevice parameter. Syntax is:
–usbdevice  host:1234:5678,
where 1234=vendor id, and 5678=product id.

But there is a problem if you have two *identical* USB devices (e.g. two smartcard readers, or two USB mice), in which case it's not possible to direct one USB device to virtual machine 1 and the second USB device to virtual machine 2. This happens for *identical* USB devices, where the vendor id and the product id is the same for botth.

In Virtualbox for example it's possible to distingish those devices. They realized it by adding a third parameter, the Serial number of the USB device.
This value is given in the "lsusb" output as "iSerial" field.

How reproducible:
Just add two identical USB devices (e.g. smartcard readers or USB mice from the same vendor) and try to pass each of them to different virtual machines.


Additional info:
My proposal is, that in qemu-kvm the --usbdevice parameter should be extended like this
--usbdevice host:<vendor id>[:<product id>[:<serial number>]

In addition corresponing options to select that in virt-manager would be helpful as well.