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virtio-rng: fix DMA alignment for data buffer

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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_group_begin()/end() annotations to place these
in distinct cache lines.

Message-ID: <157a63b6324d1f1307ddd4faa3b62a8b90a79423.1767601130.git.mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Michael S. Tsirkin
2025-12-29 18:27:21 -05:00
parent 2678369e8e
commit bd2b617c49
1 changed files with 3 additions and 0 deletions
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3
drivers/char/hw_random/virtio-rng.c
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@@ -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>
@@ -28,11 +29,13 @@ struct virtrng_info {
unsigned int data_avail;
unsigned int data_idx;
/* minimal size returned by rng_buffer_size() */
__dma_from_device_group_begin();
#if SMP_CACHE_BYTES < 32
u8 data[32];
#else
u8 data[SMP_CACHE_BYTES];
#endif
__dma_from_device_group_end();
};
static void random_recv_done(struct virtqueue *vq)