Re: [Xen-devel] [Patch] common/memory: Fix ABI breakage for XENMEM_add_to_physmap

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-01-14 at 20:21 +0000, Andrew Cooper wrote:
>   caused by c/s 4be86bb194e25e46b6cbee900601bfee76e8090a
> 
> In public/memory.h, struct xen_add_to_physmap has 'space' as an unsigned int,
> but struct xen_add_to_physmap_batch has 'space' as a uint16_t.
> 
> By defining xenmem_add_to_physmap_one() with space defined as uint16_t, the
> now-common xenmem_add_to_physmap() implicitly truncates xatp->space from
> unsigned int to uint16_t, which changes the space switch()'d upon.
> 
> This wouldn't be noticed with any upstream code (of which I am aware), but was
> discovered because of the XenServer support for legacy Windows PV drivers,
> which make XENMEM_add_to_physmap hypercalls using spaces with the top bit set.
> The current Windows PV drivers don't do this any more, but we 'fix' Xen to
> support running VMs with out-of-date tools.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Keir Fraser <keir@xxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> 
> ---
> 
> As this breakage was caused between 4.4-rc1 and -rc2,

That's certainly a good indicator, but you've not covered the actual
risks and rewards of making this change now:
http://wiki.xen.org/wiki/Xen_Roadmap/4.4#Exception_guidelines_for_after_the_code_freeze

Please can you do so.



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