How do I investigate an unresponsive KVM guest?-Collection of common programming errors

What steps can I take to investigate a KVM guest that freezes about once every two weeks? By “freezes”, I mean there is no response when I try to connect with “ssh” or “virsh console”. The host is Ubuntu (natty, 11.04), using libvirt to manage its guests, and the guest is Ubuntu (natty, 11.04), both server editions with no window manager installed.

If I force the guest to reset, it works fine for another week. There are no recent or relevant message in the guest syslog (to indicate a kernel panic, etc). For all I know, it could be that the virtual network and tty are breaking and stopping me from talking to the guest. The host runs three other, nearly identical, guests that have been stable all year. If the guest itself is crashing, shouldn’t there be some indication in syslog?

The disk is an lvm logical volume configured with virtio

% cat /etc/libvirt/qemu/vm-et.xml

    
      vm-et
      8df572f1-e1dc-275a-4b9f-b7c322e2f5d3
      2048576
      2048576
      1
      
        hvm
        
      
      
        
      
      
      destroy
      restart
      destroy
      
        /usr/bin/kvm