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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Thu, 22 Sep 2016 18:47:26 +1000
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Subject: Re: [Qemu-devel] pseries-2.6 migration from QEMU-2.6 to QEMU-2.7
 broken
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To: bharata@linux.vnet.ibm.com
Cc: qemu-devel@nongnu.org, qemu-ppc@nongnu.org, david@gibson.dropbear.id.au, clg@kaod.org, "Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>

On Thu, 2016-09-22 at 11:45 +0530, Bharata B Rao wrote:
> On Thu, Sep 22, 2016 at 04:07:21PM +1000, Benjamin Herrenschmidt wrote:
> > 
> > On Thu, 2016-09-22 at 10:51 +0530, Bharata B Rao wrote:
> > > 
> > > The flag values are expected to remain same for a machine version for
> > > the migration to succeed, but this expectation is broken now. Should
> > > we make the addition of these flags conditional on machine type
> > > version ?
> > > But these flags are part of POWER8 CPU definition which is common for
> > > both pseries and upcoming powernv.
> > 
> > Does this affect KVM ? (And if yes why on earth would KVM give a flying
> > f*** about the TCG instruction flags ?) ... If not, then I think we can
> > safely not care.
> 
> Yes, KVM migration is broken.

Argh then ... stupid design in QEMU. We can't fix anything without
breaking migration, yay !

I don't know what to do to fix that to be honest. Do we have a way to filter
what flags actually matter and filter things out when KVM is enabled ?

Ben.