Comment # 8 on bug 863991 from Lin Ma

If plugging a usb 3.0 device into a usb 3.0 port on host and passthru this
device to a guest which doesn't have xhci controller, The device is invisible
to guest, It's expected behavior because it's a speed mismatch.

Changing usb controller to '3.0' in vm details page of virt-manager makes it
work.

But it exposed another issue: the usb device won't be re-attach to kernel once
speed mismatch occured, I already sent this issue to upstream, will fix it
according to feedback.