Re: ppc pbr403 vmstate

[David Gibson]

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.

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.

-- 
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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