@planedrop Ok, so it's a host lockup rather than a crash. That's a bit more irritating to debug.
First of all, can you update to the debug hypervisor. Adjust the /boot/xen.gz -> $foo symlink to use the version of Xen with the -d.gz suffix. This is the same hypervisor changeset but with assertions and extra verbosity enabled.
Also, can you append ,keep to Xen's vga= option on the command line. This should cause Xen to keep on writing out onto the screen even after dom0 has started up. Depending on the system, this might be a bit glacial, but dom0 will come up eventually.
Then reproduce the hang. Hopefully there'll be some output from Xen before the system locks up. You might also want to consider adding noreboot to Xen's command line too, especially if there's a backtrace and you want to take a photo of it to attach here.
@olivierlambert Yea, I have bonded networks. I do rename them so that I know what they are for. It seems that the bond number (bond 1 and bond 0) changes on different servers, as I asked about before, so the name and description is needed here to make it easier.