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

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Date:   Sun, 17 Apr 2022 17:30:27 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
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 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 Sun, Apr 17, 2022 at 04:58:29PM +0800, Herbert Xu wrote:
> On Sun, Apr 17, 2022 at 09:50:50AM +0100, Catalin Marinas wrote:
> >
> > Right, if that's what you prefer. Something like:
> > 
> > diff --git a/include/linux/crypto.h b/include/linux/crypto.h
> > index 2324ab6f1846..bb645b2f2718 100644
> > --- a/include/linux/crypto.h
> > +++ b/include/linux/crypto.h
> > @@ -645,7 +645,7 @@ struct crypto_tfm {
> >  	
> >  	struct crypto_alg *__crt_alg;
> >  
> > -	void *__crt_ctx[] CRYPTO_MINALIGN_ATTR;
> > +	void *__crt_ctx[] __aligned(ARCH_DMA_MINALIGN);
> >  };
> > 
> > But once we do that, are there any other CRYPTO_MINALIGN left around?
> 
> This is still implying the whole structure is aligned to the given
> value, which it is not.
> 
> Please just add the padding as needed.

Do you mean as per Ard's proposal here:

https://lore.kernel.org/r/CAMj1kXH0x5Va7Wgs+mU1ONDwwsazOBuN4z4ihVzO2uG-n41Kbg@mail.gmail.com

struct crypto_request {
	union {
		struct {
			... fields ...
		};
		u8 __padding[ARCH_DMA_MINALIGN];
	};
	void __ctx[]  __aligned(CRYPTO_MINALIGN);
};

If CRYPTO_MINALIGN is lowered to, say, 8 (to be the same as lowest
ARCH_KMALLOC_MINALIGN), the __alignof__(req->__ctx) would be 8.
Functions like crypto_tfm_ctx_alignment() will return 8 when what you
need is 128. We can change those functions to return ARCH_DMA_MINALIGN
instead or always bump cra_alignmask to ARCH_DMA_MINALIGN-1.

-- 
Catalin