Thanks for your PR, and sorry for the delay!
I've rebased it over current master to fix conflicts.
I don't use Xen but reading your changes and the documentation, it looks good.
Please test on some Xen systems if you can, it would be good to have confirmation that it works well before I tag the next release!

With Xen 4.12 on Ubuntu 18.04 the hypervisor is not recognized.
All pgrep-commands give empty results (line 3900ff).
Only the grep-command for "hypervisor" in /proc/cpuinfo gives an positive result, but is removed in new version. (dmesg is truncated and will not help).
Kelly.

Maybe pgrep for "xenstored" can help?

I tried to install Xen, after rebooting I had a qemu process so that's strange it's not catched on your system.
To be on the safe side, I added xenstored and xenconsoled, and also the 2 kthreads created by xen, xenbus and xenwatch.
Can you try with latest master?

Yes! Well done. Thank you very much:

• This system is a host running a hypervisor: YES

You added in your grep also xenbus and xenwatch in lines 3902 and 3908 - but they are running on DomU either. So every Xen-Guest ist recognised as Xen-Dom0. Can you please remove these two search-items? Thank you.

@werk21 removed in latest commit.