[PATCH RFC 11/13] virtio-rng: fix DMA alignment for data buffer

[Michael S. Tsirkin]

The data buffer in struct virtrng_info is used for DMA_FROM_DEVICE via
virtqueue_add_inbuf() and shares cachelines with the adjacent
CPU-written fields (data_avail, data_idx).

The device writing to the DMA buffer and the CPU writing to adjacent
fields could corrupt each other's data on non-cache-coherent platforms.

Add __dma_from_device_aligned_begin annotation to place these
in distinct cache lines.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 drivers/char/hw_random/virtio-rng.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index dd998f4fe4f2..fb3c57bee3b1 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -11,6 +11,7 @@
 #include <linux/spinlock.h>
 #include <linux/virtio.h>
 #include <linux/virtio_rng.h>
+#include <linux/dma-mapping.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 
@@ -28,6 +29,7 @@ struct virtrng_info {
 	unsigned int data_avail;
 	unsigned int data_idx;
 	/* minimal size returned by rng_buffer_size() */
+	__dma_from_device_aligned_begin
 #if SMP_CACHE_BYTES < 32
 	u8 data[32];
 #else
-- 
MST