?Get the uuid of your VM (ensure that xentools is installed)
?Shutdown the VM (otherwise, unexpected problems may occur)
?Open the console of sever and enter: xe vm-param-set uuid=<VM uuid> platform:usb=true platform:usb_tablet=true
?Start the VM: xe vm-start uuid=xxx
原文：http://blog.51cto.com/kuazhang/2336051