[libvirt-users] How to explain this libvirt oddity w.r.t machine types?

Context: The baremetal host previously had QEMU 2.11. But I manually downgraded the QEMU version (via `dnf downgrade qemu-system-x86`); now it is at 2.10: $ rpm -q qemu-system-x86 qemu-system-x86-2.10.2-1.fc27.x86_64 The guest is offline. Let's see (in a couple of ways) what machine type it has while it is dormant: # virsh dumpxml cirros | grep -i machine= <type arch='x86_64' machine='pc-i440fx-2.10'>hvm</type> # grep machine= /etc/libvirt/qemu/cirros.xml <type arch='x86_64' machine='pc-i440fx-2.10'>hvm</type> Okay, now edit the guest XML and carefully remove the "machine='pc-i440fx-2.10'" bit---to see what machine type will libvirt (libvirt-daemon-kvm-4.0.0-2.fc27.x86_64) default to: # virsh edit cirros Domain cirros XML configuration edited. Now check the machine type again. Bizarrely enough, libvirt "helpfully" auto-adds QEMU *2.11* machine type, which is obviously no longer on the system! # grep machine= /etc/libvirt/qemu/cirros.xml <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type> # virsh dumpxml cirros | grep -i machine= <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type> How to explain this? Is this even a "valid test"? (To undo the nuisance, obviously, I had to `virsh edit cirros` again and change it to 2.10.) Note, I *don't* have 2.11 QEMU on the system: # rpm -qa | grep -E 'qemu.*2.11' # echo $? 1 * * * It's getting late, and I should stop staring at screens. -- /kashyap