I have been using KVM on my Ubuntu Karmic installation for some time now. I have a Windows guest which I start from time to time to perform some tedious tasks which require Microsoft products. So far KVM has worked flawlessly for me and I have come to prefer it to other solutions like VMWare.
Today I needed a 64bit Ubuntu 8.04 system to test something. Installing an Ubuntu 8.04_amd64 server guest in KVM was a matter of 10 minutes. The installation went smoothly and everything looked well but after rebooting the new system the guest would hang at the Kernel message “Loading Hardware Drivers”. I tried booting serveral times. I tried booting into recovery mode. The KVM process and virt-manager locked up every time and I needed to kill -9 them. I did a few quick searches on google but could not come up with anything.
Frustrated I started to remove virtual hardware from the guest system. After removing the Serial Interface and the Sound Card the guest would suddenly boot without any sign of trouble.
I am still not sure which of the two pieces of hardware caused the problem. Perhaps I will try to reproduce the error later and file a bug when I find the time . For now I am just happy this works..