Re: [PATCH v1 0/2] s390x/cpumodel: Introduce "best" model variants

[Peter Maydell <peter.maydell@linaro.org>]

On Mon, 18 Nov 2019 at 10:56, David Hildenbrand <david@redhat.com> wrote:
>
> On 18.11.19 11:53, Peter Maydell wrote:
> > On Mon, 18 Nov 2019 at 10:47, David Hildenbrand <david@redhat.com> wrote:
> >> My personal opinion: "max" really means "all features". If we want an
> >> automatic way to specify something you requested ("give me something
> >> that's going to work") we either have to change the definition of the
> >> max model for alla rchitectures or introduce something that really
> >> matches the "no -cpu specified" - e.g., "best".
> >
> > I don't strongly object to 'max' including deprecated features,
> > but I do definitely object to 'max' including by default any
> > experimental (x- prefix) features. Those should never be
> > enabled (whatever the '-cpu foo' name) unless the user has
> > specifically opted into them: that's the point of the x- prefix.
> > We need to be able to tell from the command line whether it's
> > got any non-standard weirdness enabled.
>
> I'll let Eduardo respond to that, as we don't really have experimental
> features on s390x, especially under KVM ("host" corresponds to "max").

Yeah, I would expect that if the kernel has fixed the KVM
interface to a feature then it wouldn't be experimental.
Experimental mostly will apply to TCG, where we might
have implementations based on a draft version of an
architecture specification (like the riscv hypervisor spec)
that could incompatibly change in future.

thanks
-- PMM