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

Maxime Ripard
2014-10-31T10:00:06Z

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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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