What do you mean? Updates for my vm are made directly in the xml file, why rebooting?
I tried adding it directly with :
<hostdev mpde="subsystem" type="usb">
<adress bus="1" port="2"/>
But same result, vm boots but none of the usb port is forwarded, i'm confuse, and libvirt documentation doesn't have an example on how to add a specific usb port from a controller.