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Date: Wed, 17 Jan 2018 20:20:29 +0100
From: Igor Mammedov <imammedo@redhat.com>
Message-ID: <20180117202029.79633974@redhat.com>
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Subject: Re: [Qemu-devel] [qemu-s390x] [PATCH 12/24] s390x: cpu: add
 TARGET_DEFAULT_CPU_TYPE macro
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To: David Hildenbrand <david@redhat.com>
Cc: qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>, qemu-s390x@nongnu.org, Laurent Vivier <laurent@vivier.eu>, Richard Henderson <rth@twiddle.net>

On Wed, 17 Jan 2018 17:04:31 +0100
David Hildenbrand <david@redhat.com> wrote:

> On 17.01.2018 16:43, Igor Mammedov wrote:
> > it will be used for for 2 purposes, 1st is to
> > provide to cpu name resolving class for machine 'none'
> >   cpu_parse_cpu_model(machine_class->default_cpu_type, cpu_model)
> > and later to drop a bunch of ifdefs *-user/main.c that
> > set default cpu_model.
> > 
> > Use default value from linux-user for TARGET_DEFAULT_CPU_TYPE.
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> > CC: Richard Henderson <rth@twiddle.net>
> > CC: Alexander Graf <agraf@suse.de>
> > CC: qemu-s390x@nongnu.org
> > ---
> >  target/s390x/cpu.h | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> > index 1a8b6b9..174624a 100644
> > --- a/target/s390x/cpu.h
> > +++ b/target/s390x/cpu.h
> > @@ -731,6 +731,7 @@ void s390_set_qemu_cpu_model(uint16_t type, uint8_t gen, uint8_t ec_ga,
> >  
> >  #define S390_CPU_TYPE_SUFFIX "-" TYPE_S390_CPU
> >  #define S390_CPU_TYPE_NAME(name) (name S390_CPU_TYPE_SUFFIX)
> > +#define TARGET_DEFAULT_CPU_TYPE S390_CPU_TYPE_NAME("qemu")
> >  
> >  /* you can call this signal handler from your SIGBUS and SIGSEGV
> >     signal handlers to inform the virtual CPU of exceptions. non zero
> >   
> 
> At least from a !KVM perspective this is correct. And that is at least
> relevant for linux-user. I doubt that this is relevant for KVM. The
> "none" machine cannot be used either way and CPU models are sensed via qmp.
If you look at cpu_parse_cpu_model() impl., you'll see that
TARGET_DEFAULT_CPU_TYPE isn't used as actual CPU type but as a proxy
to get access to CPUClass::class_by_name() callback which is
implemented by every target. So accelerator doesn't have any effect
here.

> Reviewed-by: David Hildenbrand <david@redhat.com>
Thanks!