On Thu, Jun 17, 2021 at 04:14:17PM +0200, Markus Armbruster wrote:
> Claudio Fontana <cfontana@xxxxxxx> writes:
>
> > On 6/17/21 1:09 PM, Markus Armbruster wrote:
> >> Valeriy Vdovin <valeriy.vdovin@xxxxxxxxxxxxx> writes:
> >>
> >>> On Thu, Jun 17, 2021 at 07:22:36AM +0200, Markus Armbruster wrote:
> >>>> Valeriy Vdovin <valeriy.vdovin@xxxxxxxxxxxxx> writes:
> >>>>
> >>>>> Introducing new qapi method 'query-kvm-cpuid'. This method can be used to
> >>>>
> >>>> It's actually a QMP command. There are no "qapi methods".
> >>>>
> >>>>> get virtualized cpu model info generated by QEMU during VM initialization in
> >>>>> the form of cpuid representation.
> >>>>>
> >>>>> Diving into more details about virtual cpu generation: QEMU first parses '-cpu'
> >>>>
> >>>> virtual CPU
> >>>>
> >>>>> command line option. From there it takes the name of the model as the basis for
> >>>>> feature set of the new virtual cpu. After that it uses trailing '-cpu' options,
> >>>>> that state if additional cpu features should be present on the virtual cpu or
> >>>>> excluded from it (tokens '+'/'-' or '=on'/'=off').
> >>>>> After that QEMU checks if the host's cpu can actually support the derived
> >>>>> feature set and applies host limitations to it.
> >>>>> After this initialization procedure, virtual cpu has it's model and
> >>>>> vendor names, and a working feature set and is ready for identification
> >>>>> instructions such as CPUID.
> >>>>>
> >>>>> Currently full output for this method is only supported for x86 cpus.
> >>>>
> >>>> Not sure about "currently": the interface looks quite x86-specific to me.
> >>>>
> >>> Yes, at some point I was thinking this interface could become generic,
> >>> but does not seem possible, so I'll remove this note.
> >>>
> >>>> The commit message doesn't mention KVM except in the command name. The
> >>>> schema provides the command only if defined(CONFIG_KVM).
> >>>>
> >>>> Can you explain why you need the restriction to CONFIG_KVM?
> >>>>
> >>> This CONFIG_KVM is used as a solution to a broken build if --disable-kvm
> >>> flag is set. I was choosing between this and writing empty implementation into
> >>> kvm-stub.c
> >>
> >> If the command only makes sense for KVM, then it's named correctly, but
> >> the commit message lacks a (brief!) explanation why it only makes for
> >> KVM.
> >
> >
> > Is it meaningful for HVF?
>
> I can't see why it couldn't be.
Should I also make some note about that in the commit message?
>
> Different tack: if KVM is compiled out entirely, the command isn't
> there, and trying to use it fails like
>
> {"error": {"class": "CommandNotFound", "desc": "The command query-kvm-cpuid has not been found"}}
>
> If KVM is compiled in, but disabled, e.g. with -machine accel=tcg, then
> the command fails like
>
> {"error": {"class": "GenericError", "desc": "VCPU was not initialized yet"}}
>
> This is misleading. The VCPU is actually running, it's just the wrong
> kind of VCPU.
>
> >> If it just isn't implemented for anything but KVM, then putting "kvm"
> >> into the command name is a bad idea. Also, the commit message should
> >> briefly note the restriction to KVM.
>
> Perhaps this one is closer to reality.
>
I agree.
What command name do you suggest?
> >> Pick one :)
> >>
> >> [...]
>
