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Re: [Xen-devel] [for-4.7] x86/emulate: synchronize LOCKed instruction emulation

On 04/26/16 19:03, George Dunlap wrote:
> On 19/04/16 17:35, Jan Beulich wrote:
>>>>> Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx> 04/19/16 1:01 PM >>>
>>> I think this might be because the LOCK prefix should guarantee that the
>>> instruction that follows it has exclusive use of shared memory (for both
>>> reads and writes) but I might be misreading the docs:
>> LOCK definitely has no effect on other than the instruction it gets applied
>> to.
> Sorry I wasn't involved in this discussion -- what was the conclusion here?
> FWIW Andy's suggestion of using a stub seemed like the most robust
> solution, if that could be made to work.
> If you're going to submit a patch substantially similar to this one, let
> me know so I can review the mm bits of the original patch.

I'm not really sure.

Regarding this version of the patch, Jan has asked for more information
on the performance impact, but I'm not sure how to obtain it in a
rigorous manner. If it is decided that a version of this patch is
desirable, I can go on fixing the issues we've found and address the
comments we've had so far and submit a new version.

I'm not familiar with what the stub solution would imply, so I'm afraid
I can't comment on that. This is not code I've had that much contact
with prior to stumbling into this problem.


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