Comment 16 for bug 1673467

On x86 due to a compat fix host-model effectively is CUSTOM see qemuProcessUpdateGuestCPU (in coreys post).

I also checked where this gets populated but didn't find a sweet sport to see if is now different.
But qemuBuildCpuModelArgStr was interesting.

On 2.5 and master stripped of unimportant to aarch64 it is:
- host-passthrough -> add "host"
- host-model -> fail
  (remember x86 converts host-model to custom)
- custom -> add "whatever was given"

So that won't work even if we would let it pass the check.

And while the code changed the semantics did not - yet there it handled host-model "like" passthrough not in the construction but due to a fallback in detection.

That known I checked the qemu command strings it constructed in the past, it was: "-cpu host".
Aha, no specials due to host-model (as it didn't work), so on aarch64 host-model was equal to host-passthrough with the failure that the "advertised" extra that host-model has over host-passthrough did not work.

Now libvirt changed to know that and tells you that host-model is not working, but that is actually correct - even it seemed so in the first place I'd not consider this a regression in the usual sense.

- Regression: sometihng that worked now fails
- This: something that you thought works, but didn't now fails telling you so

Summarizing in next comment to catch everybody and sync with the openstack Team on this.