Re: [PATCH 5/5] i386: provide simple 'hyperv=on' option to x86 machine types

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Igor Mammedov <imammedo@redhat.com> writes:

> On Tue, 05 Jan 2021 12:50:05 +0100
>
> I think there is a misunderstanding, idea was:
>
> cpu_initfn() {
>     //current set
>     cpu->default_hyperv_cpu_features = ACD
> }
>
> compat_props_5.1 {
>    cpu.default_hyperv_cpu_features = AB
> }
>
> compat_props_5.2 {
>    cpu.default_hyperv_cpu_features = ABC
> }
>

...

> I was talking about CPU features/properties only, it doesn't apply to other devices.
> It makes sense for machine to have a knob to create onboard hyperv specific
> devices if there is any (do we have any?).
>
> If there aren't any currently, I wouldn't bother with machine knob
> and just use -cpu foo,hv_default=on or -device cpu,hv_default=on
> like any other cpu feature.
>

We don't currently have any devices which are not 'CPU features' (in
QEMU terminology), however, we already have Vmbus and I can easily
imagine us implementing e.g. hartbeat/kvp/vss/... devices on top. We
*may* want to enable these 'automatically' and that's what make
'-machine' option preferable. It is, however, not a *must* right now and
we can indeed wait until these devices appear and be happy with
'hv_default' -cpu option for now. We will, however, need to teach upper
layers about the change when/if it happens.

-- 
Vitaly