Re: [Qemu-devel] [PATCH 0/6] pc: bring ACPI table size below to 2.0 levels, try fixing -initrd for good

[Paolo Bonzini]

Il 02/10/2014 15:41, Michael S. Tsirkin ha scritto:
> On Thu, Oct 02, 2014 at 03:30:57PM +0200, Paolo Bonzini wrote:
>> These patches do fix John's scenario, but that is not the main issue.
>> They are not an _attempt_ to fix it, they just do so more or less by
>> chance.  Their real purpose is fixing the second issue:
>>
>>> - table size changes cause cross version migration issues
>>>   this is really due to the fact we are using RAM
>>>   to migrate ACPI tables.
>>>   IMHO a more robust fix would be to allow RAM size to change
>>>   during migration, or to avoid using RAM, switch to another type of
>>>   object.
>>
>> Allowing fw_cfg size to change during migration (does not matter if it
>> is stored in RAM or otherwise) is a huge can of worms because the host
>> might have loaded the size and stored it somewhere, way before migration.
> 
> Right. I'm not suggesting it. I suggest migrating fw cfg size instead.
> 
> The issue is that incoming migration might have a different
> fw_cfg size from what we have.

Understood now.

> I think migrating this value will solve the issue in a cleaner way.

Perhaps.  The question is whether it would complicate the
forwards-migration code beyond what is sane.  I think we are practically
speaking stuck with RAM.

Paolo