Re: [PATCH v2 01/15] dma-mapping: add __dma_from_device_group_begin()/end()

Marek Szyprowski
2026-01-05T18:27:40Z

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@redhat.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@samsung.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