Re: [Xen-devel] [PATCH 03/17] xen: arm32: ensure cmpxchg has full barrier semantics

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 03/20/2014 03:45 PM, Ian Campbell wrote:
> Unrelated reads/writes should not pass the xchg.
> 
> Provide cmpxchg_local for parity with arm64, although it appears to be unused.
> It also helps make the reason for the separation of __cmpxchg_mb more
> apparent.
> 
> With this our cmpxchg is in sync with Linux v3.14-rc7.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> ---
> We got our cmpxchg implementation from Linux which AFAICS has always had these
> additional barriers. I don't recall us having decided that Xen barriers should
> not have this property as well, and if we did we were remiss in not adding a
> comment etc... If my memory is faulty then I am happy to replace thispatch
> with one which adds a comment instead.

I think the barrier is good for Xen. We may have some place where both
of this macro are used as a "barrier".

Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>

Regards,

-- 
Julien Grall

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