linux-kernel - [PATCH RFC 09/13] virtio_input: fix DMA alignment for evts

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Message-ID: <5f57d7dc13920517b3ed3e56d815ad1ba4cf36ce.1767089672.git.mst@redhat.com>
Date: Tue, 30 Dec 2025 05:16:14 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Cong Wang <xiyou.wangcong@...il.com>, Jonathan Corbet <corbet@....net>,
	Olivia Mackall <olivia@...enic.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Jason Wang <jasowang@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Gerd Hoffmann <kraxel@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
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	linux-doc@...r.kernel.org, linux-crypto@...r.kernel.org,
	virtualization@...ts.linux.dev, linux-scsi@...r.kernel.org,
	iommu@...ts.linux.dev, kvm@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH RFC 09/13] 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_aligned_begin/end annotations to ensure evts is
isolated in its own cachelines.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/virtio/virtio_input.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/virtio/virtio_input.c b/drivers/virtio/virtio_input.c
index d0728285b6ce..774494754a99 100644
--- 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_aligned_begin
 	struct virtio_input_event  evts[64];
+	__dma_from_device_aligned_end
 	spinlock_t                 lock;
 	bool                       ready;
 };
-- 
MST