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From:   Christoph Hellwig <hch@lst.de>
To:     Marek Szyprowski <m.szyprowski@samsung.com>
Cc:     Huacai Chen <chenhc@lemote.com>, Christoph Hellwig <hch@lst.de>,
        Robin Murphy <robin.murphy@arm.com>,
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        linux-scsi@vger.kernel.org, Tejun Heo <tj@kernel.org>,
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Subject: Re: [PATCH V8 4/5] libsas: Align SMP req/resp to
        dma_get_cache_alignment()
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On Tue, Oct 17, 2017 at 01:55:43PM +0200, Marek Szyprowski wrote:
> If I remember correctly, kernel guarantees that each kmalloced buffer is
> always at least aligned to the CPU cache line, so CPU cache can be
> invalidated on the allocated buffer without corrupting anything else.

Yes, from slab.h:

/*
 * Some archs want to perform DMA into kmalloc caches and need a guaranteed
 * alignment larger than the alignment of a 64-bit integer.
 * Setting ARCH_KMALLOC_MINALIGN in arch headers allows that.
 */
#if defined(ARCH_DMA_MINALIGN) && ARCH_DMA_MINALIGN > 8
#define ARCH_KMALLOC_MINALIGN ARCH_DMA_MINALIGN
#define KMALLOC_MIN_SIZE ARCH_DMA_MINALIGN
#define KMALLOC_SHIFT_LOW ilog2(ARCH_DMA_MINALIGN)
#else
#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)
#endif

Mips sets this for a few subarchitectures, but it seems like you need
to set it for yours as well.