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From: Andrew Lutomirski <luto@mit.edu>
Date: Tue, 31 May 2011 09:17:39 -0400
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Subject: Re: [PATCH 0/5] x86-64: Remove syscall instructions at fixed addresses
To: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
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On Tue, May 31, 2011 at 9:11 AM, Ingo Molnar <mingo@elte.hu> wrote:
>
> * Andrew Lutomirski <luto@mit.edu> wrote:
>
>> > You could start with picking the more compatible alternative
>> > instruction initially. I don't at all mind losing half a cycle of
>> > performance in that case ... this code should be secure first.
>>
>> The more compatible one is mfence, which in some cases could (I
>> think) be a lot more than half a cycle.
>
> I'd still suggest to do the mfence change now and remove the
> alternatives patching for now - if it's more than half a cycle then
> it sure will be implemented properly, right?

I don't know.  I just cut 5 ns off the thing a couple weeks ago and no
one beat me to it :)

I'll take a look at how hard the patching will be.

--Andy

>
> Thanks,
>
>        Ingo
>