linux-kernel - Re: [PATCH] crypto: serpent - add x86

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Date:	Thu, 31 May 2012 07:29:11 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Johannes Goetzfried 
	<Johannes.Goetzfried@...ormatik.stud.uni-erlangen.de>,
	Jussi Kivilinna <jussi.kivilinna@...et.fi>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	Tilo Müller 
	<Tilo.Mueller@...ormatik.uni-erlangen.de>
Subject: Re: [PATCH] crypto: serpent - add x86_64/avx assembler
 implementation

On Wed, May 30, 2012 at 05:39:49PM +0200, Andi Kleen wrote:
> > I agree with that. Currently when I boot my PC with a new 3.4 kernel all the
> > ciphers from the intel-aesni module get loaded whether I need them or not. As
> > Jussi stated most people using distros probably won't need the
> > serpent-avx-x86_64 module get loaded automatically, so it's probably better to
> > leave it that way.
> 
> That means you got a 50% chance to use the wrong serpent.

You should always get the best one available.  For example, when
you request for "aes" all implementations of it will be loaded by
modprobe.

> This was a continuous problem with AESNI and the accelerated CRC,
> that is why the cpuid probing was implemented.

The only case where it doesn't work is if you have some variants
built-in and the faster ones built as modules.  But then the answer
is to either build all of them as modules or all of them built-in
so that priority-based selection can work.

Can you provide an example where it doesn't work as intended?

What we could do is to use the cpuid-based probing when an algorithm
is needed to selectively load the relevant implementations instead
of all of them.  However, for most algorithms it won't make that
big a difference since all the available ones will be loaded anyway.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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