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 handles small and mergeable packets separately and fixes
the mismatched buffer address.

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 <redacted>
Signed-off-by: Jiahui Cen <redacted>
Signed-off-by: Ying Fang <redacted>
---
 drivers/net/virtio_net.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c6af18948..cbc3c0ae4 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -891,6 +891,23 @@ static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
        return buf;
 }

+static void *virtnet_rq_get_buf_small(struct receive_queue *rq,
+                                     u32 *len,
+                                     void **ctx,
+                                     unsigned int header_offset)

+{
+       void *buf;
+       unsigned int xdp_headroom;
+
+       buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
+       if (buf) {
+               xdp_headroom = (unsigned long)*ctx;
+               virtnet_rq_unmap(rq, buf + VIRTNET_RX_PAD + xdp_headroom, *len);
+       }
+
+       return buf;
+}
+
 static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
 {
        struct virtnet_rq_dma *dma;

@@ -2692,13 +2709,23 @@ static int virtnet_receive_packets(struct virtnet_info *vi,
        int packets = 0;
        void *buf;

-       if (!vi->big_packets || vi->mergeable_rx_bufs) {
+       if (vi->mergeable_rx_bufs) {
                void *ctx;
                while (packets < budget &&
                       (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
                        receive_buf(vi, rq, buf, len, ctx, xdp_xmit, stats);
                        packets++;
                }
+       } else if (!vi->big_packets) {
+               void *ctx;
+               unsigned int xdp_headroom = virtnet_get_headroom(vi);
+               unsigned int header_offset = VIRTNET_RX_PAD + xdp_headroom;
+
+               while (packets < budget &&
+                      (buf = virtnet_rq_get_buf_small(rq, &len, &ctx, header_offset))) {
+                       receive_buf(vi, rq, buf, len, ctx, xdp_xmit, stats);
+                       packets++;
+               }
        } else {
                while (packets < budget &&
                       (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
--

2.20.1