linux-kernel - Re: [RFC PATCH crypto] AES: Add support to Intel AES-NI instructions

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Message-ID: <20081216233128.GA13942@gondor.apana.org.au>
Date:	Wed, 17 Dec 2008 10:31:28 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Huang Ying <ying.huang@...el.com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Sebastian Andrzej Siewior <linux-crypto@...breakpoint.cc>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [RFC PATCH crypto] AES: Add support to Intel AES-NI
	instructions

On Mon, Dec 15, 2008 at 11:38:01PM +1100, Herbert Xu wrote:
> On Mon, Dec 15, 2008 at 04:21:06PM +1100, Herbert Xu wrote:
> >
> > > a. Do not touch SSE state in soft_irq
> > > b. Disable/restore soft_irq in kernel_fpu_begin/kernel_fpu_end
> > > c. Use a per-CPU data structure to save kernel FPU state during
> > > soft_irq.
 
> Here's another option
> 
> d. When we're in interrupt context, schedule a task to perform
> the encryption asynchronously.

We can also hybridise b. and d.:

e. When we're in interrupt context, if TS is clear, then we defer
the operation to a thread.  Otherwise if user-space has touched
the FPU we save the state, if not then we simply clear TS.  In
either case we perform the operation immediately and then reset
TS if user-space didn't touch the FPU.

This is based on the fact that it should be fairly rare for us
to interrupt a kernel FPU/SSE operation.  The common case would
be interrupting a user process or a kernel context which is not
engaging in any kernel FPU operations.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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