Re: [Qemu-devel] [PATCH v2 for-1.6 0/2] future proof rom loading for cross versiom migration

[Michael S. Tsirkin]

On Mon, Aug 12, 2013 at 09:15:55PM +0300, Michael S. Tsirkin wrote:
> Changes from v1: address comments by Peter Maydell
>     - drop useless data=data line
>     - rename target_page_size to migration_page_size to make use clear
>     Peter, you also suggested somehow hiding this within memory core.
>     I don't see a clean way to do this without lots of code
>     changes, I think what I propose here is acceptable for 1.6
>     and we can rework APIs in time for 1.7.
> 
> Please review, and consider for 1.6.

This was stuck in my outbound mail queue - wrote this
before I saw Anthony nack this change for 1.6.

So pls ignore the 1.6 tag and review for 1.7.

Thanks, and sorry about the noise.

> Original cover letter below.
> 
> ROM files that are put in FW CFG are copied to guest ram, by BIOS, but
> they are not backed by RAM so they don't get migrated.
> 
> Each time we'll change at least two bytes in such a ROM this will break
> cross-version migration: since we can migrate after BIOS has read the first
> byte but before it has read the second one, getting an inconsistent state.
> 
> This patchset makes QEMU future-proof against such changes.
> 
> Naturally, this only helps for -M 1.6 and up, older machine types
> will still have the cross-version migration bug.
> 
> I think this should be applied for 1.6, this way we won't
> have this problem from 1.7 and on.
> 
> Michael S. Tsirkin (2):
>   memory: export migration page size
>   loader: put FW CFG ROM files into RAM
> 
>  arch_init.c           |  3 +++
>  hw/core/loader.c      | 53 
> ++++++++++++++++++++++++++++++++++++++++++++++++---
>  hw/i386/pc_piix.c     |  2 ++
>  hw/i386/pc_q35.c      |  2 ++
>  include/exec/memory.h |  1 +
>  include/hw/loader.h   |  1 +
>  6 files changed, 59 insertions(+), 3 deletions(-)
> 
> -- 
> MST
>