Re: [Qemu-devel] [PATCH v3 0/2] future proof rom loading for cross versiom migration

[Laszlo Ersek <lersek@redhat.com>]

On 08/13/13 00:43, Michael S. Tsirkin wrote:
> Changes from v2: address comments on v2 by Peter Maydell
>     - switch from global constant to function
>     - use memory_region_init_ram instead of _ram_ptr
>     - disable for 1.6
> 
> 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 now
>     and we can always rework APIs without wire format changes.
> 
> Please review, and consider for merging.
> 
> 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           |  6 ++++++
>  hw/core/loader.c      | 54 ++++++++++++++++++++++++++++++++++++++++++++++++---
>  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, 63 insertions(+), 3 deletions(-)
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>