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

[Michael S. Tsirkin]

On Thu, Oct 02, 2014 at 03:43:35PM +0200, Paolo Bonzini wrote:
> 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

Migrating RAM size is actually useful too, I think someone asked for it.

-- 
MST