linux-kernel - Re: [PATCH 0/5] x86-64: Remove syscall instructions at fixed addresses

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Message-ID: <BANLkTimqf7HY9AnMDjPr197m4LrA4qJNkg@mail.gmail.com>
Date:	Tue, 31 May 2011 09:17:39 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>
Subject: Re: [PATCH 0/5] x86-64: Remove syscall instructions at fixed addresses

On Tue, May 31, 2011 at 9:11 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Andrew Lutomirski <luto@....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
>
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