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Date: Tue, 05 Mar 2013 09:24:24 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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To: Hu Tao <hutao@cn.fujitsu.com>
CC: kvm list <kvm@vger.kernel.org>, qemu-devel <qemu-devel@nongnu.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Daniel P. Berrange" <berrange@redhat.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Jan Kiszka <jan.kiszka@siemens.com>, Gleb Natapov <gleb@redhat.com>,
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        Andrew Jones <drjones@redhat.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        Sasha Levin <levinsasha928@gmail.com>,
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        "Michael S. Tsirkin" <mst@redhat.com>, Alexander Graf <agraf@suse.de>,
        Alex Williamson <alex.williamson@redhat.com>,
        Peter Maydell <peter.maydell@linaro.org>
Subject: Re: [PATCH v13 1/8] save/load cpu runstate
References: <cover.1362051581.git.hutao@cn.fujitsu.com> <df20999140db716e8b1ccd57a7cbcb0fa343a78c.1362051582.git.hutao@cn.fujitsu.com> <513469C8.30602@redhat.com> <20130305023308.GK16362@localhost.localdomain>
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Il 05/03/2013 03:33, Hu Tao ha scritto:
> On Mon, Mar 04, 2013 at 10:30:48AM +0100, Paolo Bonzini wrote:
>> Il 28/02/2013 13:13, Hu Tao ha scritto:
>>> This patch enables preservation of cpu runstate during save/load vm.
>>> So when a vm is restored from snapshot, the cpu runstate is restored,
>>> too.
>>
>> I don't think this feature is worth breaking backwards migration
>> compatibility.  It is usually handled at a higher-level (management,
>> like libvirt).
> 
> If guest panic happens during migration, runstate will still be running
> on destination host without this patch. But, it does be a problem to break
> backwards migration compatibility.

Yes, but the source management (libvirt for example) will have the
occasion to observe the change and cancel the migration or forward the
information on the wire.  There are already similar reasons why libvirt
always starts guests with -S.

Paolo