I wonder if there's an easy way to convert libvirt BIOS-based VMs into UEFI VMs if I'm willing to completely destroy their disks. Deleting and recreating everything is kind of tedious.
@cks Changing the VM itself is pretty trivial, getting the existing system to boot may be more challenging.
I'm not sure the UEFI firmware can do classic bios, it might?
I can whip up a command to do the conversion but I'm not at a laptop right now

@Lalufu It turns out you can 'just' edit the XML, but I haven't tried to see if the result will boot a MBR disk. If there's an easier way than hand-editing the XML, I'm quite interested because I have a bunch of machines to (eventually¹) do this to.

¹ some of the machines are on an Ubuntu 22.04 host that doesn't have a new enough libvirt. They'll have to move when that machine goes to 26.04.

@cks I'll have a look, but this being XML you can automate changes with a large variety of tools
@cks Which, don't get me wrong, is one of the nice things about libvirt, as soon as you've navigated the treacherous shoals of "there's an XML that defines the machine, and there's an XML that describes a currently running machine and they're related and almost identical but not the same"