[$] Virtio without the "virt"

When virtiowas merged in Linux v2.6.24, its author, Rusty Russell, described the goal as being for "common drivers to be efficiently usedacross most virtual I/O mechanisms". Today, much progress has been made toward that goal, with virtiosupported by multiple hypervisors and guest drivers shipped by many operatingsystems. But these applications of virtio are implemented in software, whereasMichael Tsirkin's "VirtIOwithout the Virt" talk at KVM Forum 2019 laid out howto implement virtio in hardware.