The document discusses running OSv (a lightweight hypervisor) on BitVisor (a virtualization platform). It summarizes steps taken to implement a virtual Virtio NIC on BitVisor by faking the PCI configuration space, memory mapped I/O, and interrupts of the physical NIC (PRO/1000) to appear as a Virtio NIC to the OSv hypervisor. This allows OSv network drivers to function without modification by redirecting requests to the real NIC through hooks installed by BitVisor.