If your mouse pointer fails to track your cursor in a VNC Viewer session in a hardware virtualized guest, add the following to the Oracle VM Server configuration file located at /etc/xen/xend-config.sxp to force the device model to use absolute (tablet) coordinates:

usbdevice='tablet'

Restart the Oracle VM Server for the changes to take effect. You may need to do this for each Oracle VM Server in the server pool.