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

["Michael S. Tsirkin" <mst@redhat.com>]

Add __dma_from_device_aligned_begin annotation before the data buffer
in struct virtrng_info to ensure proper cacheline alignment on
non-cache-coherent platforms.

The data buffer is used for DMA_FROM_DEVICE via virtqueue_add_inbuf()
and is adjacent to CPU-written fields (data_avail, data_idx). Without
proper alignment, the device writing to the DMA buffer and the CPU
writing to adjacent fields could corrupt each other's data on
platforms where DMA cache maintenance is at cacheline granularity.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 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