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

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Message-ID: <20260105104036.09a77f13@mordecai>
Date: Mon, 5 Jan 2026 10:40:36 +0100
From: Petr Tesarik <ptesarik@...e.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-kernel@...r.kernel.org, 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>, Marek Szyprowski <m.szyprowski@...sung.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>, Leon Romanovsky
 <leon@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>, Bartosz Golaszewski
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 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 Mon, 5 Jan 2026 03:22:54 -0500
"Michael S. Tsirkin" <mst@...hat.com> 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>

LGTM. I'm not formally a reviewer, but FWIW:

Reviewed-by: Petr Tesarik <ptesarik@...e.com>

> ---
>  include/linux/dma-mapping.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> 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)
>  {