libGL error: MESA-LOADER: failed to retrieve device informat

Mesa 18.1.3-201.1
kernel 4.17.5-1-default
libdrm 2.4.92-1.2

glxinfo | grep -i renderer
OpenGL renderer string: virgl

LIBGL_DEBUG=verbose glxgears
libGL error: MESA-LOADER: failed to retrieve device information
libGL: using driver virtio_gpu for 4
libGL: OpenDriver: trying /usr/lib64/dri/tls/virtio_gpu_dri.so
libGL: OpenDriver: trying /usr/lib64/dri/virtio_gpu_dri.so

Adding some debug drmMsg() prints, I found that the MESA-LOADER error message happens because drmGetDevice2() returns -ENODEV. And that happens because drmParseSubsystemType() returns -EINVAL.

drmParseSubsystemType() expects /sys/dev/char/DRM_MAJOR\:0/device/subsystem to be one of:
pci
usb
platform
hostix

but virtio-gpu has bus subsystem virtio:

ls -al /sys/dev/char/226\:0/device/subsystem
lrwxrwxrwx 1 root root 0 Jul 19 17:39 /sys/dev/char/226:0/device/subsystem -> ../../../../bus/virtio

ls -al /sys/dev/char/226\:128/device/subsystem
lrwxrwxrwx 1 root root 0 Jul 19 17:39 /sys/dev/char/226:128/device/subsystem -> ../../../../bus/virtio

Is this something that should be fixed in libdrm or in the virtio-gpu kernel driver?