linux-kernel - Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC

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Message-ID: <YlVSBuEqMt2S1Gi6@gondor.apana.org.au>
Date:   Tue, 12 Apr 2022 18:18:46 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Ard Biesheuvel <ardb@...nel.org>, Will Deacon <will@...nel.org>,
        Marc Zyngier <maz@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of
 ARCH_KMALLOC_MINALIGN

On Tue, Apr 12, 2022 at 11:02:54AM +0100, Catalin Marinas wrote:
>
> This series does not penalise any architecture. It doesn't even make
> arm64 any worse than it currently is.

Right, the patch as it stands doesn't change anything.  However,
it is also broken as it stands.  As I said before, CRYPTO_MINALIGN
is not something that is guaranteed by the Crypto API, it is simply
a statement of whatever kmalloc returns.

So if kmalloc is no longer returning CRYPTO_MINALIGN-aligned
memory, then those drivers that need this alignment for DMA
will break anyway.

If you want the Crypto API to guarantee alignment over and above
that returned by kmalloc, the correct way is to use cra_alignmask.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt