Re: [Qemu-devel] in a device or CPU instance init/realize, can I rely on something having the BQL or equivalent?

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 7 Dec 2017 17:26:53 +0000
Peter Maydell <peter.maydell@linaro.org> wrote:

> On 7 December 2017 at 17:13, Peter Maydell <peter.maydell@linaro.org> wrote:
> > On 7 December 2017 at 17:07, Eduardo Habkost <ehabkost@redhat.com> wrote:  
> >> On Thu, Dec 07, 2017 at 04:53:59PM +0000, Peter Maydell wrote:  
> >>> On 7 December 2017 at 16:48, Igor Mammedov <imammedo@redhat.com> wrote:  
> >>> > On Thu, 7 Dec 2017 16:05:50 +0000
> >>> > Peter Maydell <peter.maydell@linaro.org> wrote:
> >>> >  
> >>> >> Hi; I'm currently writing '-cpu max' support for ARM. For that I'd
> >>> >> like to be able to do the "probe host kernel for its supported feature
> >>> >> set" in the CPU object's instance-init function, but I'd like to do  
> >>
> >> I don't think instance_init is appropriate for that, as
> >> object_free(object_new(t)) must be always safe to call and free
> >> of side-effects for all types.  Wouldn't it work if you do that
> >> on realize?  
> >
> > I think we need the information before realize, but I'll double
> > check.  
> 
> We do need the information before realize, because the probe
> is what tells us what feature bits we need to set, and the
> ARM instance_post_init hook needs to look at those to determine
> eg which other feature bits to set and which QOM properties to
> expose as a result, and all that has to happen at init time,
> not realize time.
maybe it could be modeled after  kvm_ppc_register_host_cpu_type(),
i.e. create type with necessary feature bits set at cpu's class
init time (sort of combo of what ppc and x86 do).

i.e. one caches host's feature bits at cpu_class_init time and
then loads applies them to object instance at instance init time,
like in x86_cpu_initfn()->x86_cpu_load_def().

TBH:
 I do not recall why we have x86 max/host cpu types do feature
 loading at realize time instead of at class init like the rest
 of static cpu types.


> thanks
> -- PMM