virtio_input: fix DMA alignment for evts

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 evts array is used for DMA_FROM_DEVICE operations via
virtqueue_add_inbuf(). The adjacent lock and ready fields are written
by the CPU during normal operation. If these share cachelines with evts,
CPU writes can corrupt DMA data.

Add __dma_from_device_group_begin()/end() annotations to ensure evts is
isolated in its own cachelines.

Message-ID: <cd328233198a76618809bb5cd9a6ddcaa603a8a1.1767601130.git.mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/virtio/virtio_input.c b/drivers/virtio/virtio_input.c
index d0728285b6ce969b356563ed840e99cd0e4b1b0c..9f13de1f1d77b3bf9f6c8796d65f5975c54289e7 100644 (file)
--- a/drivers/virtio/virtio_input.c
+++ b/drivers/virtio/virtio_input.c
@@ -4,6 +4,7 @@
 #include <linux/virtio_config.h>
 #include <linux/input.h>
 #include <linux/slab.h>
+#include <linux/dma-mapping.h>
 
 #include <uapi/linux/virtio_ids.h>
 #include <uapi/linux/virtio_input.h>
@@ -16,7 +17,9 @@ struct virtio_input {
        char                       serial[64];
        char                       phys[64];
        struct virtqueue           *evt, *sts;
+       __dma_from_device_group_begin();
        struct virtio_input_event  evts[64];
+       __dma_from_device_group_end();
        spinlock_t                 lock;
        bool                       ready;
 };