linux-kernel - Re: [PATCH v5 4/4] crypto: Add Allwinner Security System crypto accelerator

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Date:	Fri, 31 Oct 2014 10:57:06 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Corentin LABBE <clabbe.montjoie@...il.com>, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	linux@....linux.org.uk, davem@...emloft.net,
	grant.likely@...aro.org, akpm@...ux-foundation.org,
	gregkh@...uxfoundation.org, joe@...ches.com,
	mchehab@....samsung.com, crope@....fi, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH v5 4/4] crypto: Add Allwinner Security System crypto
 accelerator

On Fri, Oct 31, 2014 at 04:18:03PM +0800, Herbert Xu wrote:
> On Fri, Oct 31, 2014 at 09:13:23AM +0100, Maxime Ripard wrote:
> >
> > I don't understand here. Why would other drivers *not* being affected?
> > 
> > If the scatter list passed by AF_ALG can be in highmem, I guess it's
> > the case for every driver out there. Almost every kernel code I've
> > seen so far makes the assumption that the memory it has is mapped and
> > accessible.
> > 
> > Somehow, it's the driver's fault now, and not the part of kernel that
> > actually does the allocation?
> 
> If you are implementing a crypto driver that is meant to handle
> requests from the crypto API then yes you need to handle highmem.

Is that documented somewhere?

> As I said if enough drivers are unable to address highmem and
> require copying/software fallbacks then we could provide this
> through the API and the driver would then only need to declare
> its lack of highmem support or use a helper.

On a 3.18-rc2 kernel:

$ git grep kmap -- crypto/
crypto/ahash.c:                         walk->data = kmap(walk->pg);
crypto/ahash.c:                         walk->data = kmap_atomic(walk->pg);
crypto/async_tx/async_memcpy.c:         dest_buf = kmap_atomic(dest) + dest_offset;
crypto/async_tx/async_memcpy.c:         src_buf = kmap_atomic(src) + src_offset;
crypto/scatterwalk.c:                   return kmap_atomic(scatterwalk_page(walk)) +
crypto/shash.c:                         data = kmap_atomic(sg_page(sg));
crypto/shash.c:                         data = kmap_atomic(sg_page(sg));

None of the drivers are.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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