netdev - Re: [kernel-hardening] Re: HalfSipHash Acceptable Usage

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Date:   Wed, 21 Dec 2016 11:41:28 -0500
From:   Rik van Riel <riel@...hat.com>
To:     kernel-hardening@...ts.openwall.com, Jason@...c4.com,
        linux@...encehorizons.net
Cc:     ak@...ux.intel.com, davem@...emloft.net, David.Laight@...lab.com,
        djb@...yp.to, ebiggers3@...il.com, eric.dumazet@...il.com,
        hannes@...essinduktion.org, jeanphilippe.aumasson@...il.com,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        luto@...capital.net, netdev@...r.kernel.org, tom@...bertland.com,
        torvalds@...ux-foundation.org, tytso@....edu,
        vegard.nossum@...il.com
Subject: Re: [kernel-hardening] Re: HalfSipHash Acceptable Usage

On Wed, 2016-12-21 at 10:55 -0500, George Spelvin wrote:
> Actually, DJB just made a very relevant suggestion.
> 
> As I've mentioned, the 32-bit performance problems are an x86-
> specific
> problem.  ARM does very well, and other processors aren't bad at all.
> 
> SipHash fits very nicely (and runs very fast) in the MMX registers.
> 
> They're 64 bits, and there are 8 of them, so the integer registers
> can
> be reserved for pointers and loop counters and all that.  And there's
> reference code available.
> 
> How much does kernel_fpu_begin()/kernel_fpu_end() cost?

Those can be very expensive. Almost certainly not
worth it for small amounts of data.

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