Re: [Qemu-devel] [PULL 1/2] spapr: Error out when CPU hotplug is attempted on older pseries machines

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Aug 04, 2016 at 04:14:53PM +0530, Bharata B Rao wrote:
> On Wed, Aug 03, 2016 at 03:25:50PM +1000, David Gibson wrote:
> > From: Bharata B Rao <bharata@linux.vnet.ibm.com>
> > 
> > CPU hotplug and coldplug aren't supported prior to pseries-2.7.  Further,
> > earlier machine types don't use CPU core objects at all.  These mean that
> > query-hotpluggable-cpus and coldplug on older pseries machines will crash
> > QEMU.  It also means that hotpluggable_cpus flag in query-machines will
> > be incorrectly set to true for pseries < 2.7, since it is based on the
> > presence of the query_hotpluggable_cpus hook.
> > 
> > - Don't assign the query_hotpluggable_cpus hook for pseries < 2.7
> > - query_hotpluggable_cpus should therefore never be called on pseries <
> >   2.7, so add an assert
> > - spapr_core_pre_plug() should fail hot/cold plug attempts for pseries <
> >   2.7, since core objects are never used there
> > - spapr_core_plug() should therefore never be called for pseries < 2.7, so
> >   add an assert.
> > 
> > Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> > [dwg: Change from query_hotpluggable_cpus returning NULL for pseries < 2.7
> >  to not being called at all, reword commit message for accuracy]
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  hw/ppc/spapr.c          |  7 ++++++-
> >  hw/ppc/spapr_cpu_core.c | 19 ++++++-------------
> >  2 files changed, 12 insertions(+), 14 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index fbbd051..bce2371 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -2376,8 +2376,11 @@ static HotpluggableCPUList *spapr_query_hotpluggable_cpus(MachineState *machine)
> >      int i;
> >      HotpluggableCPUList *head = NULL;
> >      sPAPRMachineState *spapr = SPAPR_MACHINE(machine);
> > +    sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(machine);
> >      int spapr_max_cores = max_cpus / smp_threads;
> > 
> > +    g_assert(smc->dr_cpu_enabled);
> > +
> >      for (i = 0; i < spapr_max_cores; i++) {
> >          HotpluggableCPUList *list_item = g_new0(typeof(*list_item), 1);
> >          HotpluggableCPU *cpu_item = g_new0(typeof(*cpu_item), 1);
> > @@ -2432,7 +2435,9 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
> >      hc->plug = spapr_machine_device_plug;
> >      hc->unplug = spapr_machine_device_unplug;
> >      mc->cpu_index_to_socket_id = spapr_cpu_index_to_socket_id;
> > -    mc->query_hotpluggable_cpus = spapr_query_hotpluggable_cpus;
> > +    if (smc->dr_cpu_enabled) {
> > +        mc->query_hotpluggable_cpus = spapr_query_hotpluggable_cpus;
> > +    }
> > 
> >      smc->dr_lmb_enabled = true;
> >      smc->dr_cpu_enabled = true;
> 
> Unfortunately smc->dr_cpu_enabled is always false when you set
> mc->query_hotpluggable_cpus and will be set to true immediately
> afterwards as seen in above hunk.
> 
> This leads to query-hotpluggable-cpus being unavailable for all
> machine type versions. Your first version of setting
> mc->query_hotpluggable_cpus to NULL explicitly for 2.6 and downwards
> was correct.

*facepalm* I can't believe I forgot to check that.


In fact.. we could just replace dr_lmb_enabled with the NULL or
not-NULL status of query_hotpluggable_cpus.

I'll send a fix shortly.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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