[SeaBIOS] vga passthrough fail

[Lying]

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>