On Fri, Nov 18, 2022 at 10:52:32AM +0100, Jiri Denemark wrote: > > * Qemu already provide an option 'enforce' to validate if features > > with which vm is started is exactly same as one provided and nothing > > is silently dropped. > > Right, but it's not enough. In addition to removed features libvirt also > checks for unexpectedly added features. And you really need to do both. > Because if you ask for -cpu Model,feat1=on,feat2=on,enforce and QEMU > says everything is fine, the guest might see more than what you asked. > For example, if a feature is enabled only if a host supports it you may > or may not get it without any complains from QEMU. But if you get it you > really need to explicitly ask for it during migration, otherwise the > feature can just silently disappear. Of course, this would be a really > bad behavior from QEMU, but that does not mean it can't happen (I think > SVM is a bit problematic in this way) and the whole point of libvirt's > checks is to prevent this kind of issues. Hi Jiri, I'm not following this very well. I think you're saying that qemu has had bugs previously where features get silently enabled, and it's libvirt's job/role to paper over those issues? Do you have some specific cases of this? thanks john
