Re: [Qemu-devel] [PATCH v4 5/6] xics: directly register ICPState objects to vmstate

[Greg Kurz]

On Mon, 12 Jun 2017 22:15:46 +0800
David Gibson <address@hidden> wrote:

> On Thu, Jun 08, 2017 at 03:43:18PM +0200, Greg Kurz wrote:
> > The ICPState objects are currently registered to vmstate as qdev objects.
> > Their instance ids are hence computed automatically in the migration code,
> > and thus depends on the order the CPU cores were plugged.
> > 
> > If the destination had its CPU cores plugged in a different order than the
> > source, then ICPState objects will have different instance_ids and load
> > the wrong state.
> > 
> > Since CPU objects have a reliable cpu_index which is already used as
> > instance_id in vmstate, let's use it for ICPState as well.
> > 
> > Signed-off-by: Greg Kurz <address@hidden>  
> 
> This is certainly an improvement.  You answered my query on the
> previous version as to why this doesn't break migration, but that
> information should go into the commit message.
> 

I'll add this explanation to the changelog.

> So, ideally, we would use the XICS "server number" as the migration
> key.  That's an architected part of the XICs state, since those values
> are entered explicitly into the ICS.  We have a way to go from server
> number to ICP at the moment, but not the reverse, but we can fix that.
> 
> Unfortunately I think those won't always match existing automatically
> generated IDs, which makes things harder.
> 

Maybe things will get better when cpu_dt_id can be contiguous:

http://www.spinics.net/lists/kvm/msg150390.html

But I guess it won't help with existing machine types.

> > ---
> >  hw/intc/xics.c |    5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/intc/xics.c b/hw/intc/xics.c
> > index 7ccfb53c55a0..faa5c631f655 100644
> > --- a/hw/intc/xics.c
> > +++ b/hw/intc/xics.c
> > @@ -344,10 +344,14 @@ static void icp_realize(DeviceState *dev, Error 
> > **errp)
> >      }
> >  
> >      qemu_register_reset(icp_reset, dev);
> > +    vmstate_register(NULL, icp->cs->cpu_index, &vmstate_icp_server, icp);
> >  }
> >  
> >  static void icp_unrealize(DeviceState *dev, Error **errp)
> >  {
> > +    ICPState *icp = ICP(dev);
> > +
> > +    vmstate_unregister(NULL, &vmstate_icp_server, icp);
> >      qemu_unregister_reset(icp_reset, dev);
> >  }
> >  
> > @@ -355,7 +359,6 @@ static void icp_class_init(ObjectClass *klass, void 
> > *data)
> >  {
> >      DeviceClass *dc = DEVICE_CLASS(klass);
> >  
> > -    dc->vmsd = &vmstate_icp_server;
> >      dc->realize = icp_realize;
> >      dc->unrealize = icp_unrealize;
> >  }
> >   
>

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