Re: ppc pbr403 vmstate

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Cédric Le Goater (clg@kaod.org) wrote:
> On 1/17/22 06:52, David Gibson wrote:
> > On Fri, Jan 14, 2022 at 08:07:21AM +0100, Cédric le Goater wrote:
> > > On 1/14/22 00:41, David Gibson wrote:
> > > > On Thu, Jan 13, 2022 at 06:51:56PM +0000, Dr. David Alan Gilbert wrote:
> > > > > Hi,
> > > > >     Is there any easy way of getting a machine where the pbr403 vmstate
> > > > > would be generated?
> > > > 
> > > > The condition in pbr403_needed is...
> > > > 
> > > >       return (pvr & 0xffff0000) == 0x00200000;
> > > > 
> > > > .. which looks to be the PVR for ppc403 models.  That makes sense with
> > > > the section name... but not so much with the fact that it's under
> > > > cpu/tlb6xx.  The 6xx MMU is basically unrelated to the 40x MMU.  But
> > > > it looks like the vmstate_tlbemb might be shared between then, because
> > > > of bad ideas of the past.
> > > > 
> > > > But in any case, we already dropped what little 403 support we ever
> > > > had - there's nothing with that PVR even listed in
> > > > target/ppc/cpu-models.h.
> > > > 
> > > > So I think we should just drop it.
> > > 
> > > yes. But we can not remove env.pb since this would break migration
> > > compatibility, correct ?
> > 
> > Only if it appears in a migration section that's actually emitted by a
> > supported machine type.  As far as I can tell the only section that
> > does that is vmstate_pbr403, which we're also dropping so we should be
> > fine.
> 
> I sent a patch to remove vmstate_pbr403 first.

Thanks!

Dave

>  > It is also touched in the *super* old cpu_load_old.  I suspect we
> > could probably just drop that completely, since I don't think we
> > realistically support migration from a version that old anyway.  But
> > even if we don't want to do that right now, we can just replace the
> > reads into env->pb with discarding reads and we'll be fine.  We don't
> > implement any cpus that actually used those fields, so we can ignore
> > them in the migration stream.
> 
> I will take a look at this also with follow ups.
> 
> Thanks,
> 
> C.
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK