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

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Date:   Fri, 15 Apr 2022 16:12:03 +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 10:05:21AM +0200, Ard Biesheuvel wrote:
>
> I guess that should be fixable. GIven that this is about padding
> rather than alignment, we could do something like
> 
> struct crypto_request {
>   union {
>       struct {
>         ... fields ...
>       };
>       u8 __padding[ARCH_DMA_MINALIGN];
>    };
>     void __ctx[]  __align(CRYPTO_MINALIGN);
> };
> 
> And then hopefully, we can get rid of the padding once we fix drivers
> doing non-cache coherent inbound DMA into those structures.

Sorry, I don't think this works.  kmalloc can still return something
that's not ARCH_DMA_MINALIGN-aligned, and therefore __ctx won't be
aligned correctly.

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