netdev - Re: [PATCH v2 01/15] dma-mapping: add __dma_from_device_group

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Message-ID: <8dbf60ac-0821-4ebf-8191-acf348525c26@samsung.com>
Date: Mon, 5 Jan 2026 19:27:29 +0100
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc: Cong Wang <xiyou.wangcong@...il.com>, Jonathan Corbet <corbet@....net>,
	Olivia Mackall <olivia@...enic.com>, Herbert Xu
	<herbert@...dor.apana.org.au>, Jason Wang <jasowang@...hat.com>, Paolo
	Bonzini <pbonzini@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>,
	Eugenio Pérez <eperezma@...hat.com>, "James E.J. Bottomley"
	<James.Bottomley@...senpartnership.com>, "Martin K. Petersen"
	<martin.petersen@...cle.com>, Gerd Hoffmann <kraxel@...hat.com>, Xuan Zhuo
	<xuanzhuo@...ux.alibaba.com>, Robin Murphy <robin.murphy@....com>, Stefano
	Garzarella <sgarzare@...hat.com>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
	Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Petr Tesarik
	<ptesarik@...e.com>, Leon Romanovsky <leon@...nel.org>, Jason Gunthorpe
	<jgg@...pe.ca>, Bartosz Golaszewski <brgl@...nel.org>,
	linux-doc@...r.kernel.org, linux-crypto@...r.kernel.org,
	virtualization@...ts.linux.dev, linux-scsi@...r.kernel.org,
	iommu@...ts.linux.dev, kvm@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 01/15] dma-mapping: add
 __dma_from_device_group_begin()/end()

On 05.01.2026 09:22, Michael S. Tsirkin wrote:
> When a structure contains a buffer that DMA writes to alongside fields
> that the CPU writes to, cache line sharing between the DMA buffer and
> CPU-written fields can cause data corruption on non-cache-coherent
> platforms.
>
> Add __dma_from_device_group_begin()/end() annotations to ensure proper
> alignment to prevent this:
>
> struct my_device {
> 	spinlock_t lock1;
> 	__dma_from_device_group_begin();
> 	char dma_buffer1[16];
> 	char dma_buffer2[16];
> 	__dma_from_device_group_end();
> 	spinlock_t lock2;
> };
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>   include/linux/dma-mapping.h | 13 +++++++++++++
>   1 file changed, 13 insertions(+)

Right, this was one of the long standing issues, how to make DMA to the 
buffers embedded into some structures safe and this solution looks 
really nice.

Acked-by: Marek Szyprowski <m.szyprowski@...sung.com>


> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index aa36a0d1d9df..29ad2ce700f0 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -7,6 +7,7 @@
>   #include <linux/dma-direction.h>
>   #include <linux/scatterlist.h>
>   #include <linux/bug.h>
> +#include <linux/cache.h>
>   
>   /**
>    * List of possible attributes associated with a DMA mapping. The semantics
> @@ -703,6 +704,18 @@ static inline int dma_get_cache_alignment(void)
>   }
>   #endif
>   
> +#ifdef ARCH_HAS_DMA_MINALIGN
> +#define ____dma_from_device_aligned __aligned(ARCH_DMA_MINALIGN)
> +#else
> +#define ____dma_from_device_aligned
> +#endif
> +/* Mark start of DMA buffer */
> +#define __dma_from_device_group_begin(GROUP)			\
> +	__cacheline_group_begin(GROUP) ____dma_from_device_aligned
> +/* Mark end of DMA buffer */
> +#define __dma_from_device_group_end(GROUP)			\
> +	__cacheline_group_end(GROUP) ____dma_from_device_aligned
> +
>   static inline void *dmam_alloc_coherent(struct device *dev, size_t size,
>   		dma_addr_t *dma_handle, gfp_t gfp)
>   {

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland