Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Date:   Thu, 7 Apr 2022 19:40:59 +0800
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>, Will Deacon <will@kernel.org>,
        Marc Zyngier <maz@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of
 ARCH_KMALLOC_MINALIGN
Message-ID: <Yk7Ny/iFi0NrMXTg@gondor.apana.org.au>
References: <20220405135758.774016-1-catalin.marinas@arm.com>
 <20220405135758.774016-8-catalin.marinas@arm.com>
 <YkzJP6zmkAhc6CI9@gondor.apana.org.au>
 <CAMj1kXEXhFmGc4VTTcJU1YFsHJhZN44OdJ5Suf2ONG5=LR29HQ@mail.gmail.com>
 <Yk1UJs6eZMoIp3Eh@arm.com>
 <Yk5o/lNTyiJWD4Ae@gondor.apana.org.au>
 <Yk7EbvYhwnQy+pAf@arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Yk7EbvYhwnQy+pAf@arm.com>
Precedence: bulk

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.

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

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