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Re: [Qemu-ppc] broken incoming migration

From: Alexey Kardashevskiy
Subject: Re: [Qemu-ppc] broken incoming migration
Date: Thu, 30 May 2013 18:18:05 +1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6

On 05/30/2013 05:49 PM, Paolo Bonzini wrote:
> 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. :)

I'll wait for 24 hours (forgot to cc: the author) and then post a revert
patch :)


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