Description of problem:
gnome-shell has black square flash when virgl has been enabled

Version-Release number of selected component (if applicable):
qemu-kvm-4.2.0-8.module+el8.2.0+5607+dc756904.x86_64
virglrenderer-0.8.1-1.module+el8.2.0+5515+afa04555.x86_64

Host gpu:
00:02.0 VGA compatible controller: Intel Corporation Iris Pro Graphics 580

How reproducible:
100%

Steps to Reproduce:
1.Boot rhel8.2 vm with below libvirt configurations:
...
    <graphics type='spice' port='5900' autoport='yes' listen='0.0.0.0'>
      <listen type='address' address='0.0.0.0'/>
      <image compression='off'/>
    </graphics>
    <graphics type='egl-headless'>
      <gl rendernode='/dev/dri/renderD128'/>
    </graphics>
    <sound model='ich9'>
      <alias name='sound0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1b' function='0x0'/>
    </sound>
    <video>
      <model type='virtio' heads='2' primary='yes'>
        <acceleration accel3d='yes'/>
      </model>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
    </video>
...
2.Connect remote-viewer to vm
3.Inside vm, open a gnome-shell terminal, input some characters. For make the issue more obvious, can input ctrl + u to clean these characters

Actual results:
gnome-shell has black square flash

Expected results:
no back square flash

Additional info:
No such issue happen after disabling virgl