Use of full virtualization with Xen/Libvirt

If you want to start a full virtualized instance on Xen (HVM) you have to set vm_mode=hvm in the properties of the used image (glance image-create/image-update ... --property vm_mode=hvm ...). If you don’t do that the start of the instance will fail with something like VmError: Boot loader didn't return any data!.