Would be handy to have <cpu mode='host-model'> support <feature policy='force'/> or policy=disable. That way tools have an option to turn on x2apic for kvm guests which provides a performance boost with no downsides, but doesn't require host CPU support.
Also <feature policy='disable'/>. For one use case, see: https://bugzilla.redhat.com/show_bug.cgi?id=870071#c2
Fixed upstream with: commit 3c8be55c04eb2647fd5c9d51efae78f7afdcec85 Author: Peter Krempa <pkrempa> Date: Mon Jul 15 17:38:55 2013 +0200 cpu: Allow fine tuning of "host-model" cpu https://bugzilla.redhat.com/show_bug.cgi?id=799354 Until now, the "host-model" cpu mode couldn't be influenced. This patch allows to use the <feature> elements to either enable or disable specific CPU flags. This can be used to force flags that can be emulated even if the host CPU doesn't support them. commit 13cdd389ed06e81277f208c269d825046cdbb4cb Author: Peter Krempa <pkrempa> Date: Mon Jul 15 14:36:09 2013 +0200 cpu: Add virCPUDefUpdateFeature() This new function updates or adds a feature to a existing cpu model definition. This function will be helpful to allow tuning of "host-model" features in later patches. v1.1.0-193-g3c8be55