ppc pbr403 vmstate

ppc pbr403 vmstate

[Dr. David Alan Gilbert]

Hi,
  Is there any easy way of getting a machine where the pbr403 vmstate
would be generated?

  Given my vague understanding of vmstate subsection naming, I think
we need:

diff --git a/target/ppc/machine.c b/target/ppc/machine.c
index 756d8de5d8..e535edb7c4 100644
--- a/target/ppc/machine.c
+++ b/target/ppc/machine.c
@@ -718,7 +718,7 @@ static bool pbr403_needed(void *opaque)
 }
 
 static const VMStateDescription vmstate_pbr403 = {
-    .name = "cpu/pbr403",
+    .name = "cpu/tlb6xx/pbr403",
     .version_id = 1,
     .minimum_version_id = 1,
     .needed = pbr403_needed,

to fit the rule where the name of a subsection is prefixed
by the parent name. (Something a new check I added just triggered).

Dave

-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Re: ppc pbr403 vmstate

[David Gibson]

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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.

>   Given my vague understanding of vmstate subsection naming, I think
> we need:
> 
> diff --git a/target/ppc/machine.c b/target/ppc/machine.c
> index 756d8de5d8..e535edb7c4 100644
> --- a/target/ppc/machine.c
> +++ b/target/ppc/machine.c
> @@ -718,7 +718,7 @@ static bool pbr403_needed(void *opaque)
>  }
>  
>  static const VMStateDescription vmstate_pbr403 = {
> -    .name = "cpu/pbr403",
> +    .name = "cpu/tlb6xx/pbr403",
>      .version_id = 1,
>      .minimum_version_id = 1,
>      .needed = pbr403_needed,
> 
> to fit the rule where the name of a subsection is prefixed
> by the parent name. (Something a new check I added just triggered).
> 
> Dave
> 

-- 
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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Re: ppc pbr403 vmstate

[Cédric Le Goater]

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 ?


I will send a patch.

Thanks,

C.

Re: ppc pbr403 vmstate

[David Gibson]

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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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Re: ppc pbr403 vmstate

[Cédric Le Goater]

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.

  > 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.

Re: ppc pbr403 vmstate

[Dr. David Alan Gilbert]

* 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

Re: ppc pbr403 vmstate

[Peter Maydell]

On Mon, 17 Jan 2022 at 05:52, David Gibson <david@gibson.dropbear.id.au> wrote:
> 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.

This would be a nice thing to do, because the PPC CPU is the
only remaining in-tree user of the .load_state_old migration
hook, so if we declared that we don't support migrating from
those old versions of QEMU (1.5 and earlier, I think) then we
could delete the .load_state_old and .minimum_version_id_old
handling completely.

-- PMM

Re: ppc pbr403 vmstate

[Cédric Le Goater]

On 1/17/22 21:40, Peter Maydell wrote:
> On Mon, 17 Jan 2022 at 05:52, David Gibson <david@gibson.dropbear.id.au> wrote:
>> 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.
> 
> This would be a nice thing to do, because the PPC CPU is the
> only remaining in-tree user of the .load_state_old migration
> hook, so if we declared that we don't support migrating from
> those old versions of QEMU (1.5 and earlier, I think) then we
> could delete the .load_state_old and .minimum_version_id_old
> handling completely.

yes. It should be fine for PPC.

Thanks,

C.