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

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Message-ID: <YllE+wWqP6F+1nwa@gondor.apana.org.au>
Date:   Fri, 15 Apr 2022 18:12:11 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        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 Memory Management List <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <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 Fri, Apr 15, 2022 at 11:51:49AM +0200, Ard Biesheuvel wrote:
>
> That is the whole point, really: ARCH_DMA_MINALIGN==128 does not mean
> __ctx needs to be aligned to 128 bytes, it only means that it should
> not share a 128 byte cacheline with the preceding fields. So if
> kmalloc() returns buffers that are aligned to whatever alignment the
> platform requires (which will be 64 in most cases), the above
> arrangement ensures that, without requiring that CRYPTO_MINALIGN ==
> ARCH_DMA_MINALIGN.

What if they started sharing a cacheline with the subsequent object?
I guess you could add some more padding at the end though.

I could accept this as a temporary solution, if you volunteer to
modify all the affected drivers so we can get rid of this bandaid.

Thanks,
-- 
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