I installed it on amd64/current(kvm guest), it work.
Host: debian/amd64
Guest: openbsd/amd64
(add 3 lines to /usr/src/sys/arch/amd64/conf/GENERIC for enable amd64)
+virtio* at pci? # Virtio PCI device
+vioblk* at virtio? # Virtio block device
+vioif* at virtio? # Virtio network device
I tested on bsd.sp and bsd.mp, both work.
I running it a week(few hours per day).
I running chrome, pf and building the kernel without a problem
I feeling bsd.mp is more fast to run chrome and xfce4.
vioif0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
lladdr 00:aa:bb:cc:dd:07
priority: 0
groups: egress
media: Ethernet autoselect
status: active
inet6 fe80::2aa:bbff:fecc:dd07%vioif0 prefixlen 64 scopeid 0x1
inet 192.168.168.107 netmask 0xffffff00 broadcast 192.168.168.255
