I have three Windows XP guests running on a recently upgraded 64-bit Ubuntu 10.04 system. Occasionally (on the order of once every few days), one of the guests will become non-responsive and the kvm process on the host which is running that guest will start consuming 100% CPU. It will continue to do so until it is killed. When restarted, it will be fine for a while, and then the issue repeats.

The kvm command line used to run all three guests is this:

/usr/bin/kvm -S -M pc-0.12 -enable-kvm -m 1024 -smp 1 -name bigdog21vmxp1 \
    -uuid ea47ff84-125b-16f7-9a4d-a6d0d8bab46a \
    -chardev socket,id=monitor,path=/var/lib/libvirt/qemu/bigdog21vmxp1.monitor,server,nowait \
    -monitor chardev:monitor \
    -localtime \
    -boot c \
    -drive file=/var/lib/libvirt/images/windowsxp-1.qcow2,if=ide,index=0,boot=on,format=qcow2 \
    -net nic,macaddr=54:52:00:02:06:0e,vlan=0,name=nic.0 \
    -net tap,fd=58,vlan=0,name=tap.0 \
    -chardev pty,id=serial0 \
    -serial chardev:serial0 \
    -parallel none \
    -usb \
    -usbdevice tablet \
    -vnc 127.0.0.1:1 \
    -k en-us \
    -vga cirrus \
    -soundhw es1370

Why do the systems misbehave this way sometimes? And what configuration can I change in order to fix it? Or, if the problem is due to a bug in kvm, what is the process for isolating a kvm failure so that the developers have a chance of fixing it?