Re: [Qemu-devel] broken incoming migration

[Alexey Kardashevskiy <aik@ozlabs.ru>]

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 :)



-- 
Alexey