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

Catalin Marinas
2022-04-07T09:25:29Z

On Thu, Apr 07, 2022 at 02:14:15PM +0800, Muchun Song wrote:
> On Tue, Apr 05, 2022 at 02:57:55PM +0100, Catalin Marinas wrote:
> > ARCH_DMA_MINALIGN represents the minimum (static) alignment for safe DMA
> > operations while ARCH_KMALLOC_MINALIGN is the minimum kmalloc() objects
> > alignment.
> >
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Herbert Xu <herbert@gondor.apana.org.au>
> > Cc: "David S. Miller" <davem@davemloft.net>
> > ---
> > include/linux/crypto.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/crypto.h b/include/linux/crypto.h
> > index 2324ab6f1846..654b9c355575 100644
> > --- a/include/linux/crypto.h
> > +++ b/include/linux/crypto.h
> > @@ -167,7 +167,7 @@
> > * maintenance for non-coherent DMA (cache invalidation in particular) does not
> > * affect data that may be accessed by the CPU concurrently.
> > */
> > -#define CRYPTO_MINALIGN ARCH_KMALLOC_MINALIGN
> > +#define CRYPTO_MINALIGN ARCH_DMA_MINALIGN
>
> I don't think this should be changed since ARCH_KMALLOC_MINALIGN is
> already aligned with the size what you need.

With this series, ARCH_KMALLOC_MINALIGN is no longer safe for
non-coherent DMA on all arm64 SoCs, that's what ARCH_DMA_MINALIGN will
cover.

Now, looking at the comment for CRYPTO_MINALIGN, one aspect it covers is
the minimum alignment required by C for the crypto_tfm structure access.
So a smaller ARCH_KMALLOC_MINALIGN would do. But the other part of the
comment mentions in-structure alignment for non-coherent DMA. Here we'd
need the upper bound alignment, ARCH_DMA_MINALIGN.

I'll follow up on Herbert's email as I think he has a good point on
structure vs kmalloc() alignment.

--
Catalin