Re: [RFC 18/21] arm/cpu: Introduce a customizable kvm host cpu model

[Cornelia Huck <cohuck@redhat.com>]

On Fri, Oct 25 2024, Daniel P. Berrangé <berrange@redhat.com> wrote:

> On Fri, Oct 25, 2024 at 03:18:25PM +0200, Eric Auger wrote:
>> Hi Daniel,
>> 
>> On 10/25/24 15:06, Daniel P. Berrangé wrote:
>> > On Fri, Oct 25, 2024 at 12:17:37PM +0200, Eric Auger wrote:
>> >> At the moment, the custom model does not support legacy options
>> >> of the host cpu model. We need to understand what we do with those
>> >> latter (SVE, ...). This means that related KVM ioctl are
>> >> not called yet.
>> > It will be pretty painful to have to use different feature
>> > terminology for different CPU models. Everything in libvirt
>> > assuming feature terminology varies per-arch, not per-CPU
>> > model.
>> Actually as far as I understand those regids/fields would fit all kind
>> of aarch64 Cortex-A CPUs. So they wouldn't vary per-CPU (I mean their
>> terminology. Their availability will).
>
> What I mean is can we define  named models for various different
> vendor's Cortex-A silicon and just use that without needing to
> toggle features, except in rare cases.

I'm not sure whether creating named models for various cpus would
actually scale; what we probably could do is come up with some Armv8.6,
Armv8.7, ... models and have additional models for some well-known cpus.
That would also give us some basic sanity checks for feature
combinations, if we do not want to support completely custom
frankencpus.