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    SubjectRe: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN
    On Thu, Apr 7, 2022 at 5:25 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
    >
    > 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.

    Got it. Now I know what you want to do. You want to set
    ARCH_KMALLOC_MINALIGN to 64, however, the smallest
    size of kmem_cache depends on the cache line size at
    runtime. But we have to know the safe alignment at building
    time. So we have to make those align with ARCH_DMA_MINALIGN.
    Right? I think you are on the right road since most CPUs have
    a 64-byte cache line.

    Thanks.

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