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

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Date:	Thu, 26 Nov 2015 16:49:13 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
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, 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,
-- 
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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