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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Wed, 04 Sep 2013 21:54:12 +1000
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Subject: Re: [Qemu-devel] [RFC PATCH] spapr: add initial ibm,
 client-architecture-support rtas call support
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To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>, Alexander Graf <agraf@suse.de>, qemu-devel@nongnu.org, qemu-ppc@nongnu.org, Paul Mackerras <paulus@samba.org>, Andreas =?ISO-8859-1?Q?F=E4rber?= <afaerber@suse.de>

On Wed, 2013-09-04 at 21:40 +1000, Alexey Kardashevskiy wrote:
> One of the examples (came from Paul) is:
> the host runs on POWER8, the guest boots a kernel which is capable of
> POWER7 only + POWER7-compat. We do this reboot tweak and boot in
> POWER7-compat mode. Then the guest does "yum update" and gets POWER8
> kernel
> installed so when it reboots, it will boot in normal POWER8 mode.
> Everybody
> is happy.
> 
> Having POWER7-compat mode set from the very beginning will break this
> behaviour.

But it will allow migrating that partition to a P7 machine. It's
important to be able to specify the compat mode for that reason, to
create guests that can be migrated to older machines.

Cheers,
Ben.