linux-kernel - Re: [RFD] Direct support for the x86 RDRAND instruction

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Message-ID: <CA+55aFwazvdePdf4ieooQH60bz69v0HNuH4g3M_9WMUVjtw86Q@mail.gmail.com>
Date:	Fri, 29 Jul 2011 23:03:24 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jeff Garzik <jgarzik@...ox.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Matt Mackall <mpm@...enic.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>,
	"Theodore Ts'o" <tytso@....edu>, linux-kernel@...r.kernel.org
Subject: Re: [RFD] Direct support for the x86 RDRAND instruction

On Fri, Jul 29, 2011 at 2:05 PM, Jeff Garzik <jgarzik@...ox.com> wrote:
>
> This does not cover the one question I [predictably] have:  why not do this
> in rngd, rather than the kernel?

So that's a silly question. It's a dichotomy that just doesn't exist.
Go ahead and use rdrand in rngd too.

But that is entirely independent of the kernel. Why should any
potential rngd use suddenly mean that the kernel shouldn't try to
improve *its* random number code?

No reason what-so-ever. rngd can do whatever the hell it wants. The
kernel doesn't care, and the kernel isn't impacted. There really is no
reason to do "either or", and they have nothing to do with each other.

The kernel also uses the "mov" instruction too to move data between
registers. Should that mean that user programs shouldn't use that
instruction? Obviously not.

               Linus
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