netdev - [RESEND PATCH v3] virtio_net: Fix mismatched buf address when unmapping for small packets

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Message-Id: <20240919081351.51772-1-liwenbo.martin@bytedance.com>
Date: Thu, 19 Sep 2024 16:13:51 +0800
From: Wenbo Li <liwenbo.martin@...edance.com>
To: mst@...hat.com,
	jasowang@...hat.com,
	xuanzhuo@...ux.alibaba.com,
	eperezma@...hat.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com
Cc: virtualization@...ts.linux.dev,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Wenbo Li <liwenbo.martin@...edance.com>,
	Jiahui Cen <cenjiahui@...edance.com>,
	Ying Fang <fangying.tommy@...edance.com>
Subject: [RESEND PATCH v3] virtio_net: Fix mismatched buf address when unmapping for small packets

Currently, the virtio-net driver will perform a pre-dma-mapping for
small or mergeable RX buffer. But for small packets, a mismatched address
without VIRTNET_RX_PAD and xdp_headroom is used for unmapping.

That will result in unsynchronized buffers when SWIOTLB is enabled, for
example, when running as a TDX guest.

This patch unifies the address passed to the virtio core as the address of
the virtnet header and fixes the mismatched buffer address.

Changes from v2: unify the buf that passed to the virtio core in small
and merge mode.
Changes from v1: Use ctx to get xdp_headroom.

Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling mergeable buffers")
Signed-off-by: Wenbo Li <liwenbo.martin@...edance.com>
Signed-off-by: Jiahui Cen <cenjiahui@...edance.com>
Signed-off-by: Ying Fang <fangying.tommy@...edance.com>
---
 drivers/net/virtio_net.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 6f4781ec2b36..f8131f92a392 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1807,6 +1807,11 @@ static struct sk_buff *receive_small(struct net_device *dev,
 	struct page *page = virt_to_head_page(buf);
 	struct sk_buff *skb;
 
+	/* We passed the address of virtnet header to virtio-core,
+	 * so truncate the padding.
+	 */
+	buf -= VIRTNET_RX_PAD + xdp_headroom;
+
 	len -= vi->hdr_len;
 	u64_stats_add(&stats->bytes, len);
 
@@ -2422,8 +2427,9 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
 	if (unlikely(!buf))
 		return -ENOMEM;
 
-	virtnet_rq_init_one_sg(rq, buf + VIRTNET_RX_PAD + xdp_headroom,
-			       vi->hdr_len + GOOD_PACKET_LEN);
+	buf += VIRTNET_RX_PAD + xdp_headroom;
+
+	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
 
 	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
 	if (err < 0) {
-- 
2.20.1