OpenBSD version 4.5 and above made changes in kernel which prevents booting OpenBSD using KVM technology. OpenBSD 4.4 runs with mbbios enabled. However, due to some sort of bug in KVM it does not boot and hangs while displaying a message which read as "Starting tty flags". The workaround is to disable mpbios. This may or may not happen with your installation, but if it hanged, use the following procedure.
Step # 1: Boot OpenBSD With -c Option
At boot> prompt type the following command:
bsd -c disable mpbios quit
Now OpenBSD will boot without any problem. Login as root and type the following command to disable mpbios permanently:
# config -ef /bsd disable mpbios quit
Now you can use OpenBSD without any problem. Please note that this problem only occured under RHEL 5.5 64bit (KVM83) running OpenBSD 4.7 64bit guest. The config command can be used to build kernel compilation directories or modify a kernel. In this case you've modified the kernel to boot without mpbios support. The mpbios driver extracts configuration information from the BIOS on multiprocessor systems that conform to the Intel MultiProcessor Specification. See config and mpbios man page for further information.
This FAQ entry is 13 of 14 in the "CentOS / Redhat (RHEL) KVM Virtulization" series. Keep reading the rest of the series: