Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN

Catalin Marinas
2022-04-07T16:28:40Z

On Thu, Apr 07, 2022 at 07:40:59PM +0800, Herbert Xu wrote:
> On Thu, Apr 07, 2022 at 12:01:02PM +0100, Catalin Marinas wrote:
> > The only issue is whether the compiler gets confused by a pointer to a
> > structure with a smaller alignment than alignof(struct ...). I don't see
> > a performance or correctness issue on arm64 here. It would be a problem
> > if instead of 16 we went down to 8 or 4 due to unaligned accesses but
> > from 128 to 64 (or even 16), I don't think it matters.
>
> The issue is that there's code in the Crypto API which assumes
> that all pointers returned by kmalloc are aligned to CRYPTO_MINALIGN,
> if you break that then all that code would need to be modified.

I'm not familiar with the crypto API, trying to make sense of it now ;).

I can see in many cases that the kmalloc() caller aligns the requested
size to something like crypto_tfm_ctx_alignment(). So this would
guarantee a kmalloc() object aligned to CRYPTO_MINALIGN.

> However, I think it's better to change the code that assumes
> CRYPTO_MINALIGN guarantees DMA alignment.

I saw Ard already started to refactor some of these. But in the meantime
are there cases where the crypto code does a kmalloc() of less than
CRYPTO_MINALIGN and expects it to be CRYPTO_MINALIGN aligned?

--
Catalin