xen

$/!\$ Since GNU Mach doesn't handle PAE yet, you'll need a PAE-disabled hypervisor.

$/!\$ You need an already installed GNU/Hurd system.

This also means that you'll currently need a PAE-disabled dom0. Stefan Siegl is providing a PAE-disabled Linux kernel image at http://brokenpipe.de/GnuHurd/XEN/.

You can either get binaries at http://youpibouh.thefreecat.org/hurd-xen/ or build them yourself.

Copy gnumach-xen and hurd-modules to your dom0 /boot.
Copy hurd into /etc/xen, edit it for fixing access to your hurd / and swap
Run xm create -c hurd, gnumach should get started.
If xm complains about networking (vif could not be connected), it's Xen scripts' fault, see Xen documentation for how to configure the network. The simplest way is network-bridge with fixed IPs (note that you need the bridge-utils package for this). You can also just disable networking by commenting the vif line in the config.
If xm complains Error: (2, 'Invalid kernel', 'xc_dom_compat_check: guest type xen-3.0-x86_32 not supported by xen kernel, sorry\n'), you most probably have a PAE-enabled hypervisor, and you just need to install and boot non-PAE hypervisor and kernel.

If you want to generate these images, first get the gnumach-1-branch-Xen-branch branch from gnumach CVS. Then look for "Ugly" in kern/bootstrap.c, how to generate hurd-modules is explained there, and you'll have to fix EXT2FS_SIZE and LD_SO_SIZE by hand. Then use

./configure --enable-platform=xen
make

The current hurd-modules was built from the debian packages hurd 20070606-2 and libc0.3 2.6.1-1. $/!\$ This means that when using this image, your GNU/Hurd system also needs to be a glibc version 2.6-based one!

Internals.

GNU Savannah task #5468, GNU Savannah task #6584.