Re: [Qemu-devel] [PATCH 0/5] pc: make ROMs resizeable

[Michael S. Tsirkin]

On Mon, Nov 17, 2014 at 10:08:46PM +0200, Michael S. Tsirkin wrote:
> At the moment we migrate ROMs which reside in fw cfg, which allows
> changing ROM code at will, and supports migrating largish blocks early,
> with good performance.
> However, we are running into a problem: changing size breaks
> migration every time.
> This already requires somewhat messy compatibility support in
> acpi generation code, and it looks like there'll be more to come.
> 
> Rather than try to guess the correct size once and for all,
> this patchset tries to make code future-proof, by
> adding support for resizeable ram blocks.
> 
> A (possibly very high) amount of space in ram_addr_t space is reserved
> for each block, but never allocated.
> If incoming block size differs from current size, block is
> reallocated. FW CFG is also notified and updated accordingly.
> 
> To simplify things, I didn't add support for resizing
> actual RAM: device RAM such as fw cfg ROMs are never mapped
> into guests directly, so instead I added an API to
> flag device RAM explicitly, and manage them using
> simple alloc/free/realloc
> 
> Considering this promises to rid us of worries about ROM size considerations
> once and for all, I thinking about pushing this as a "kind of bugfix" before
> 2.2, so we don't need to maintain more band-aids in 2.3 and on.
> 
> Note: migration stream is unaffected by these patches.
> This makes it possible to enable this functionality
> unconditionally, for all machine types.
> 
> In the future, this might be handy for other things,
> such as changing kernels loaded on command line
> across migrations.
> 
> Note: cross version migration testing still ongoing,
> I'll definitely complete that before pushing it out.

And to make it clear, I'd like to see review from
migration maintainers on this.
The patchset crosses into pc so it's probably best to
merge through my tree to avoic conflicts.


> Michael S. Tsirkin (5):
>   cpu: add cpu_physical_memory_clear_dirty_range_nocode
>   exec: qemu_ram_alloc_device, qemu_ram_resize
>   arch_init: support resizing on incoming migration
>   memory: interface to allocate device ram
>   acpi-build: make ROMs device RAM, make them resizeable
> 
>  hw/lm32/lm32_hwsetup.h  |   3 +-
>  include/exec/cpu-all.h  |   8 +++-
>  include/exec/memory.h   |  22 ++++++++++
>  include/exec/ram_addr.h |  15 +++++++
>  include/hw/loader.h     |   4 +-
>  arch_init.c             |  13 +++---
>  exec.c                  | 113 
> +++++++++++++++++++++++++++++++++++++++++++-----
>  hw/core/loader.c        |  18 ++++++--
>  hw/i386/acpi-build.c    |  19 +++++---
>  memory.c                |  17 ++++++++
>  10 files changed, 202 insertions(+), 30 deletions(-)
> 
> -- 
> MST
>