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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 21 Apr 2022 09:36:46 +0200
Message-ID: <CAK8P3a3MVZ=QGcU8DaZbc5eaAt_FvoEEnqLqTYa=+9w__VYEig@mail.gmail.com>
Subject: Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Arnd Bergmann <arnd@arndb.de>, Ard Biesheuvel <ardb@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
        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>
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On Thu, Apr 21, 2022 at 9:20 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> Btw, there is another option:  Most real systems already require having
> swiotlb to bounce buffer in some cases.  We could simply force bounce
> buffering in the dma mapping code for too small or not properly aligned
> transfers and just decrease the dma alignment.

I like the idea because these days we already rely on bounce buffering
for sub-page buffers in many iommu based cases for strict isolation
purposes, as well as most 64-bit machines that lack an iommu.

Does this work on all 32-bit architectures as well? I see that you added
swiotlb for ARM LPASE systems in 2019, but I don't know if that has any
additional requirements for the other 32-bit architectures that don't
select SWIOTLB today.

      Arnd