[PATCH RFC 07/13] vsock/virtio: fix DMA alignment for event_list

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

On non-cache-coherent platforms, when a structure contains a buffer
used for DMA alongside fields that the CPU writes to, cacheline sharing
can cause data corruption.

The event_list array is used for DMA_FROM_DEVICE operations via
virtqueue_add_inbuf(). The adjacent event_run and guest_cid fields are
written by the CPU while the buffer is available, so mapped for the
device. If these share cachelines with event_list, CPU writes can
corrupt DMA data.

Add __dma_from_device_aligned_begin/end annotations to ensure event_list
is isolated in its own cachelines.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 net/vmw_vsock/virtio_transport.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 8c867023a2e5..76099f7dc040 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -17,6 +17,7 @@
 #include <linux/virtio_ids.h>
 #include <linux/virtio_config.h>
 #include <linux/virtio_vsock.h>
+#include <linux/dma-mapping.h>
 #include <net/sock.h>
 #include <linux/mutex.h>
 #include <net/af_vsock.h>
@@ -59,8 +60,10 @@ struct virtio_vsock {
 	 */
 	struct mutex event_lock;
 	bool event_run;
+	__dma_from_device_aligned_begin
 	struct virtio_vsock_event event_list[8];
 
+	__dma_from_device_aligned_end
 	u32 guest_cid;
 	bool seqpacket_allow;
 
-- 
MST