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_aligned_begin/__dma_from_device_aligned_end
annotations to ensure proper alignment to prevent this:
struct my_device {
spinlock_t lock1;
__dma_from_device_aligned_begin char dma_buffer1[16];
char dma_buffer2[16];
__dma_from_device_aligned_end spinlock_t lock2;
};
When the DMA buffer is the last field in the structure, just
__dma_from_device_aligned_begin is enough - the compiler's struct
padding protects the tail:
struct my_device {
spinlock_t lock;
struct mutex mlock;
__dma_from_device_aligned_begin char dma_buffer1[16];
char dma_buffer2[16];
};
Signed-off-by: Michael S. Tsirkin <[email protected]>
---
include/linux/dma-mapping.h | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index aa36a0d1d9df..47b7de3786a1 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -703,6 +703,16 @@ 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
+/* Apply to the 1st field of the DMA buffer */
+#define __dma_from_device_aligned_begin ____dma_from_device_aligned
+/* Apply to the 1st field beyond the DMA buffer */
+#define __dma_from_device_aligned_end ____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
