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

Michael S. Tsirkin
2026-01-05T08:23:01Z

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(+)

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)
{
--
MST