How do I customize the virtual machine configuration XML for an HVM instance in a persistent way?

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So, I’d like to tweak the XML config being used for a HVM. I’m well aware that any changes I make to it risk reducing my overall security and/or bricking my HVM entirely; this is all in the name of experimentation and personal development.

Here’s what I’ve tried:

  • I’ve tried virsh edit from dom0; and while this works, the edits are lost after I next restart the HVM.
  • I’ve also tried creating a file in /etc/qubes/templates/libvirt/xen/by-name/my-domain.xml and then restarting the Qube to regenerate the config.
  • I’ve even tried updating /usr/share/qubes/templates/libvirt/xen.xml directly and restarting the Qube. But not even this worked.

I based these attempts off of reading this documentation: https://dev.qubes-os.org/projects/core-admin/en/latest/libvirt.html

None of these have worked - which makes me suspect I’m missing something? (Like, is libvirt or some other component somehow caching these configs?)

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So, I’ve answered my own question. (Posting for anyone in the future with a similar issue.)

It turns out that these configuration files absolutely 100% work - but that if you’re looking at the results via virsh dumpxml or virsh edit you’ll find anything libvirtd didn’t understand stripped out silently.

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