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Re: [Qemu-devel] [PATCH v3 0/8] acpi: make ROMs resizeable

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v3 0/8] acpi: make ROMs resizeable
Date: Wed, 07 Jan 2015 21:48:36 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0

On 07/01/2015 20:48, Michael S. Tsirkin wrote:
> This is v3 of the patchset.
> Changes since v2:
>     - Address Paolo's comments: drop an unused function, fix up
>       comment.
> Changes since v1:
>     - Any RAM can now be resizeable - there's no requirement
>       that it's device RAM any longer.
>     - For simplicity, max_size RAM is always pre-allocated
>     - Added memory_region_set_size, to keep MR size consistent
>       in case MR is guest visible (even though for current users,
>       it never is)
> 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.
> While recent patches by Paolo and others might make it easier
> to keep table size static for specific machine types, having
> a safety net in case we do need to change it sounds like
> a good idea.
> 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
> and allocated in host for each block, but never used by fw cfg.
> If incoming block size differs from current size, block is
> reallocated. FW CFG is also notified and updated accordingly.
> As reviewers felt that making all RAM "resizeable" in this
> way might make debugging migration harder, these patches
> set a per-block flag and only allow resizing for blocks
> where this was explicitly requested.
> 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 API might be handy for other things, besides ROMs.

Ok for 2.3, just squash 4 and 8 together.  No need to repost.

Reviewed-by: Paolo Bonzini <address@hidden>

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