Re: [PATCH 1/4] block: use ARCH_KMALLOC_MINALIGN as the default dma pad mask

[FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>]

On Wed, 21 May 2008 19:25:54 +0800
Herbert Xu <herbert@gondor.apana.org.au> wrote:

> On Wed, May 21, 2008 at 08:01:12PM +0900, FUJITA Tomonori wrote:
> >
> > Why do algorithms require alignments bigger than ARCH_KMALLOC_MINALIGN?
> 
> Because the hardware may require it.  For example, the VIA Padlock
> will fault unless the buffers are 16-byte aligned (it being an
> x86-32 platform).

OK, thanks. So it's about hardware requrement. Let me make sure if I
understand crypto alignment issue.

__crt_ctx needs ARCH_KMALLOC_MINALIGN alignment only because of crypto
hardware. If I misunderstand it, can you answer my question in the
previous mail (it's the part that you cut)? That is, why does
__crt_ctx need ARCH_KMALLOC_MINALIGN alignment with software
algorithms.

The VIA Padlock likes 16-byte aligned __crt_ctx. On x86-32 platform,
ARCH_KMALLOC_MINALIGN is not defined, so __crt_ctx is 8-byte
aligned. struct aes_ctx of The VIA Padlock may not be aligned so you
may need ALIGN hack every time.

But ARCH_KMALLOC_MINALIGN is 128 bytes on some architectures. In this
case, __crt_ctx is 128-byte aligned and struct aes_ctx of The VIA
Padlock is guaranteed to be aligned nicely.