netdev - Re: [PATCH] crypto: aesni-intel

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Date:	Sat, 15 Nov 2014 11:15:50 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	Ming Liu <ming.liu@...driver.com>, davem@...emloft.net,
	ying.xue@...driver.com, linux-crypto@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] crypto: aesni-intel - avoid IPsec re-ordering

On Wed, Nov 12, 2014 at 09:41:38AM +0100, Steffen Klassert wrote:
>
> Everything below the local_bh_enable() should not run in atomic context
> as the subsequent functions may set the CRYPTO_TFM_REQ_MAY_SLEEP flag.

Actually I'm thinking of doing exactly that (disabling softirq in
cryptd) to fix the reordering problem.

Most threads do not use the FPU/SIMD so cryptd is only ever needed
when we have a user-space app that touches the FPU/SIMD which then
gets an interrupt to perform crypto in softirq.  So forcing cryptd
on everyone just because some apps touch the FPU/SIMD is a non-
starter.

The most straightforward solution is to always defer to cryptd once
it gets started.  This is bad because if a rarely used app that
touches FPU/SIMD runs then we'll end up stuck in cryptd long after
the app goes away.

So what I'm thinking of is to have the softirq path forcibly regain
control from cryptd where possible.  This is tricky because cryptd
might be in the middle of processing a request.  So that's why I'd
like to disable softirqs while we're processing a request.

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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