libvirt users - Nov 2017 - vga passthroufh fail

Hello, I encounter a problem, my display is not light when guest running.


But it's successful that i check guest with command "ping".


Following message is my xml and refer topic from
https://libvirt.org/formatdomain.html#elementsHostDev:
<hostdev mode='subsystem' type='pci'
managed='yes'>
 <driver name='vfio' />
    <source>
      <address domain='0x0000' bus='0x06' slot='0x02'
function='0x0'/>
    </source>

</hostdev>