CONFIG_VIRTIO (not configurable)

modulename: virtio.ko

configname: CONFIG_VIRTIO

Linux Kernel Configuration
└─>Device Drivers
└─>VIRTIO
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
This option is selected by any driver which implements the virtio
bus, such as CONFIG_VIRTIO_PCI, CONFIG_VIRTIO_MMIO, CONFIG_LGUEST,
CONFIG_RPMSG or CONFIG_S390_GUEST.

source code:
drivers/virtio/
is selected by
CONFIG_VIRTIO_NET