Pkg xen devel - Dec 2013 - Bug#731038: xen-utils-4.3: cannot create hwm

You should post your xlexample.hvm file.  Nonetheless, I have something 
like this in my file.

device_model_version="qemu-xen"
device_model_override="/usr/bin/qemu-system-x86_64"
builder='hvm'

Please reply if this does or does not work for you.

I think that Debian's xen hvm support is either broken or very poorly 
documented.

Marc