Re: [Qemu-devel] [RFC PATCH v1 3/5] spapr: Implement CPUClass::get_migration_id() for PowerPC CPUs

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Wed, Jul 06, 2016 at 02:01:14PM +0200, Igor Mammedov wrote:
> On Wed,  6 Jul 2016 14:29:19 +0530
> Bharata B Rao <bharata@linux.vnet.ibm.com> wrote:
> 
> > cpu_index is used as migration_id by default. For machine type
> > versions that set use-migration-id property, cpu_dt_it is returned.
> > 
> > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> > ---
> >  target-ppc/translate_init.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/target-ppc/translate_init.c b/target-ppc/translate_init.c
> > index efd6b88..9ca2f5e 100644
> > --- a/target-ppc/translate_init.c
> > +++ b/target-ppc/translate_init.c
> > @@ -10359,6 +10359,17 @@ static gchar *ppc_gdb_arch_name(CPUState *cs)
> >  #endif
> >  }
> >  
> > +static int ppc_cpu_get_migration_id(CPUState *cs)
> > +{
> > +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> > +
> > +    if (cs->use_migration_id) {
> > +        return (int) cpu->cpu_dt_id;
> Could cpu_dt_id have value bigger than 32bit int? If yes, it's not safe
> to do so, that's the reason why I'm going to use index in possible_cpus
> on ARM and for the sake of uniformity do the same for x86 (even though
> it's possible to use 32bit APIC ID).

For the existing max_cpus limit, 32 bit should be fine, but obviously
that is not good and future safe.

I had a brief look at the implementation around possible_cpus in
x86, let me see if I can do something similar for generating stable
ids for PowerPC. I thought device tree ID would be our stable id, but
that being 64 bit and migration code requiring 32 bit value isn't
helping :(

Regards,
Bharata.