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Date: Thu, 30 May 2013 09:49:51 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] broken incoming migration
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To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, David Gibson <david@gibson.dropbear.id.au>

Il 30/05/2013 09:44, Alexey Kardashevskiy ha scritto:
> Hi!
> 
> I found the migration broken on pseries platform, specifically, this patch
> broke it:
> 
> f1c72795af573b24a7da5eb52375c9aba8a37972
> migration: do not sent zero pages in bulk stage
> 
> The idea is not to send zero pages to the destination guest which is
> expected to have 100% empty RAM.
> 
> However on pseries plaftorm the guest always has some stuff in the RAM as a
> part of initialization (device tree, system firmware and rtas (?)) so it is
> not completely empty. As the source guest cannot detect this, it skips some
> pages during migration and we get a broken destination guest. Bug.
> 
> While the idea is ok in general, I do not see any easy way to fix it as
> neither QEMUMachine::init nor QEMUMachine::reset callbacks has information
> about whether we are about to receive a migration or not (-incoming
> parameter) and we cannot move device-tree and system firmware
> initialization anywhere else.
> 
> ram_bulk_stage is static and cannot be disabled from the platform
> initialization code.
> 
> So what would the community suggest?

Revert the patch. :)

Paolo