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Date:   Tue, 10 May 2022 18:10:34 +0100
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>
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 Memory Management List <linux-mm@kvack.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>
Subject: Re: [RFC PATCH 2/7] crypto: api - Add crypto_tfm_ctx_dma
Message-ID: <Ynqciq2p8mtTg98n@arm.com>
References: <YnpGnsr4k7yVUR54@gondor.apana.org.au>
 <E1noNhu-00BzV4-4N@fornost.hmeau.com>
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Hi Herbert,

Thanks for putting this together.

On Tue, May 10, 2022 at 07:07:10PM +0800, Herbert Xu wrote:
> diff --git a/include/crypto/algapi.h b/include/crypto/algapi.h
> index f50c5d1725da5..cdf12e51c53a0 100644
> --- a/include/crypto/algapi.h
> +++ b/include/crypto/algapi.h
> @@ -189,10 +189,34 @@ static inline void crypto_xor_cpy(u8 *dst, const u8 *src1, const u8 *src2,
>  	}
>  }
>  
> +static inline void *crypto_tfm_ctx(struct crypto_tfm *tfm)
> +{
> +	return tfm->__crt_ctx;
> +}
> +
> +static inline void *crypto_tfm_ctx_align(struct crypto_tfm *tfm,
> +					 unsigned int align)
> +{
> +	if (align <= crypto_tfm_ctx_alignment())
> +		align = 1;
> +
> +	return PTR_ALIGN(crypto_tfm_ctx(tfm), align);
> +}
> +
>  static inline void *crypto_tfm_ctx_aligned(struct crypto_tfm *tfm)
>  {
> -	return PTR_ALIGN(crypto_tfm_ctx(tfm),
> -			 crypto_tfm_alg_alignmask(tfm) + 1);
> +	return crypto_tfm_ctx_align(tfm, crypto_tfm_alg_alignmask(tfm) + 1);
> +}
> +
> +static inline void *crypto_tfm_ctx_dma(struct crypto_tfm *tfm)
> +{
> +	unsigned int align = 1;
> +
> +#ifdef ARCH_DMA_MINALIGN
> +	align = ARCH_DMA_MINALIGN;
> +#endif
> +
> +	return crypto_tfm_ctx_align(tfm, align);
>  }

Is there a case where a driver needs the minimum alignment between
ARCH_DMA_MINALIGN and crypto_tfm_alg_alignmask()+1? Maybe for platforms
where ARCH_DMA_MINALIGN is 8 (fully coherent) but the device's bus
master alignment requirements are higher.

My plan is to have ARCH_DMA_MINALIGN always defined but potentially
higher than ARCH_KMALLOC_MINALIGN on specific architectures. I think
crypto_tfm_ctx_dma() should use ARCH_KMALLOC_MINALIGN (and no #ifdefs)
until I get my patches sorted and I'll replace it with ARCH_DMA_MINALIGN
once it's defined globally (still no #ifdefs). Currently in mainline
it's ARCH_KMALLOC_MINALIGN that gives the static DMA alignment.

With the explicit crypto_tfm_ctx_dma(), can CRYPTO_MINALIGN_ATTR be
dropped entirely? This may be beneficial in reducing the structure size
when no DMA is required.

-- 
Catalin