Re: [PATCH v2 01/15] dma-mapping: add __dma_from_device_group_begin()/end()
From: Marek Szyprowski <m.szyprowski@samsung.com>
Date: 2026-01-05 18:27:40
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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>
quoted hunk ↗ jump to hunk
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