Re: [Qemu-devel] broken incoming migration

[Alexey Kardashevskiy <aik@ozlabs.ru>]

Forgot some cc:.

On 05/30/2013 05:44 PM, Alexey Kardashevskiy wrote:
> 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? Thanks!
> 
> 


-- 
Alexey