linux-kernel - Re: [PATCH v3 5/5] crypto: AES CBC multi-buffer glue code

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Date:	Wed, 02 Dec 2015 12:03:58 -0800
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"David S.Miller" <davem@...emloft.net>,
	Stephan Mueller <smueller@...onox.de>,
	Chandramouli Narayanan <mouli_7982@...oo.com>,
	Vinodh Gopal <vinodh.gopal@...el.com>,
	James Guilford <james.guilford@...el.com>,
	Wajdi Feghali <wajdi.k.feghali@...el.com>,
	Jussi Kivilinna <jussi.kivilinna@....fi>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/5] crypto: AES CBC multi-buffer glue code

On Tue, 2015-12-01 at 09:19 -0800, Tim Chen wrote:
> On Thu, 2015-11-26 at 16:49 +0800, Herbert Xu wrote:
> > On Tue, Nov 24, 2015 at 10:30:06AM -0800, Tim Chen wrote:
> > >
> > > On the decrypt path, we don't need to use multi-buffer algorithm
> > > as aes-cbc decrypt can be parallelized inherently on a single
> > > request.  So most of the time the outer layer algorithm
> > > cbc_mb_async_ablk_decrypt can bypass mcryptd and
> > > invoke mb_aes_cbc_decrypt synchronously
> > > to do aes_cbc_dec when fpu is available.
> > > This avoids the overhead of going through mcryptd.  Hence
> > > the use of blkcipher on the inner layer.  For the mcryptd
> > > path, we will complete a decrypt request in one shot so
> > > blkcipher usage should be fine.
> > 
> > I think there is a misunderstanding here.  Just because you're
> > using/exporting through the ablkcipher interface doesn't mean
> > that you are asynchrounous.  For example, all blkcipher algorithms
> > can be accessed through the ablkcipher interface and they of course
> > remain synchrounous.
> > 
> > So I don't see how using an ablkcipher in the inner layer changes
> > anything at all.  You can still return immediately and not bother
> > with completion functions when you are synchrounous.
> > 
> > Cheers,
> 
> OK, I'll try to see if I can cast things back to the original ablkcipher
> request and use that to walk the sg list.
> 

Herbert,

I've sent out a new version of this series to use ablkcipher on the
inner layer of decrypt.  Thanks.

Tim

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