virtio_net: xsk: rx: support recv small mode

In the process:
1. We may need to copy data to create skb for XDP_PASS.
2. We may need to call xsk_buff_free() to release the buffer.
3. The handle for xdp_buff is difference from the buffer.

If we pushed this logic into existing receive handle(merge and small),
we would have to maintain code scattered inside merge and small (and big).
So I think it is a good choice for us to put the xsk code into an
independent function.
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://patch.msgid.link/20240708112537.96291-10-xuanzhuo@linux.alibaba.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/virtio_net.c

@@ -498,6 +498,12 @@ struct virtio_net_common_hdr {
 };
 
 static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
+static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
+			       struct net_device *dev,
+			       unsigned int *xdp_xmit,
+			       struct virtnet_rq_stats *stats);
+static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *rq,
+				 struct sk_buff *skb, u8 flags);
 
 static bool is_xdp_frame(void *ptr)
 {
@@ -1062,6 +1068,124 @@ static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
 	sg->length = len;
 }
 
+static struct xdp_buff *buf_to_xdp(struct virtnet_info *vi,
+				   struct receive_queue *rq, void *buf, u32 len)
+{
+	struct xdp_buff *xdp;
+	u32 bufsize;
+
+	xdp = (struct xdp_buff *)buf;
+
+	bufsize = xsk_pool_get_rx_frame_size(rq->xsk_pool) + vi->hdr_len;
+
+	if (unlikely(len > bufsize)) {
+		pr_debug("%s: rx error: len %u exceeds truesize %u\n",
+			 vi->dev->name, len, bufsize);
+		DEV_STATS_INC(vi->dev, rx_length_errors);
+		xsk_buff_free(xdp);
+		return NULL;
+	}
+
+	xsk_buff_set_size(xdp, len);
+	xsk_buff_dma_sync_for_cpu(xdp);
+
+	return xdp;
+}
+
+static struct sk_buff *xsk_construct_skb(struct receive_queue *rq,
+					 struct xdp_buff *xdp)
+{
+	unsigned int metasize = xdp->data - xdp->data_meta;
+	struct sk_buff *skb;
+	unsigned int size;
+
+	size = xdp->data_end - xdp->data_hard_start;
+	skb = napi_alloc_skb(&rq->napi, size);
+	if (unlikely(!skb)) {
+		xsk_buff_free(xdp);
+		return NULL;
+	}
+
+	skb_reserve(skb, xdp->data_meta - xdp->data_hard_start);
+
+	size = xdp->data_end - xdp->data_meta;
+	memcpy(__skb_put(skb, size), xdp->data_meta, size);
+
+	if (metasize) {
+		__skb_pull(skb, metasize);
+		skb_metadata_set(skb, metasize);
+	}
+
+	xsk_buff_free(xdp);
+
+	return skb;
+}
+
+static struct sk_buff *virtnet_receive_xsk_small(struct net_device *dev, struct virtnet_info *vi,
+						 struct receive_queue *rq, struct xdp_buff *xdp,
+						 unsigned int *xdp_xmit,
+						 struct virtnet_rq_stats *stats)
+{
+	struct bpf_prog *prog;
+	u32 ret;
+
+	ret = XDP_PASS;
+	rcu_read_lock();
+	prog = rcu_dereference(rq->xdp_prog);
+	if (prog)
+		ret = virtnet_xdp_handler(prog, xdp, dev, xdp_xmit, stats);
+	rcu_read_unlock();
+
+	switch (ret) {
+	case XDP_PASS:
+		return xsk_construct_skb(rq, xdp);
+
+	case XDP_TX:
+	case XDP_REDIRECT:
+		return NULL;
+
+	default:
+		/* drop packet */
+		xsk_buff_free(xdp);
+		u64_stats_inc(&stats->drops);
+		return NULL;
+	}
+}
+
+static void virtnet_receive_xsk_buf(struct virtnet_info *vi, struct receive_queue *rq,
+				    void *buf, u32 len,
+				    unsigned int *xdp_xmit,
+				    struct virtnet_rq_stats *stats)
+{
+	struct net_device *dev = vi->dev;
+	struct sk_buff *skb = NULL;
+	struct xdp_buff *xdp;
+	u8 flags;
+
+	len -= vi->hdr_len;
+
+	u64_stats_add(&stats->bytes, len);
+
+	xdp = buf_to_xdp(vi, rq, buf, len);
+	if (!xdp)
+		return;
+
+	if (unlikely(len < ETH_HLEN)) {
+		pr_debug("%s: short packet %i\n", dev->name, len);
+		DEV_STATS_INC(dev, rx_length_errors);
+		xsk_buff_free(xdp);
+		return;
+	}
+
+	flags = ((struct virtio_net_common_hdr *)(xdp->data - vi->hdr_len))->hdr.flags;
+
+	if (!vi->mergeable_rx_bufs)
+		skb = virtnet_receive_xsk_small(dev, vi, rq, xdp, xdp_xmit, stats);
+
+	if (skb)
+		virtnet_receive_done(vi, rq, skb, flags);
+}
+
 static int virtnet_add_recvbuf_xsk(struct virtnet_info *vi, struct receive_queue *rq,
 				   struct xsk_buff_pool *pool, gfp_t gfp)
 {
@@ -2392,32 +2516,68 @@ static void refill_work(struct work_struct *work)
 	}
 }
 
-static int virtnet_receive(struct receive_queue *rq, int budget,
-			   unsigned int *xdp_xmit)
+static int virtnet_receive_xsk_bufs(struct virtnet_info *vi,
+				    struct receive_queue *rq,
+				    int budget,
+				    unsigned int *xdp_xmit,
+				    struct virtnet_rq_stats *stats)
+{
+	unsigned int len;
+	int packets = 0;
+	void *buf;
+
+	while (packets < budget) {
+		buf = virtqueue_get_buf(rq->vq, &len);
+		if (!buf)
+			break;
+
+		virtnet_receive_xsk_buf(vi, rq, buf, len, xdp_xmit, stats);
+		packets++;
+	}
+
+	return packets;
+}
+
+static int virtnet_receive_packets(struct virtnet_info *vi,
+				   struct receive_queue *rq,
+				   int budget,
+				   unsigned int *xdp_xmit,
+				   struct virtnet_rq_stats *stats)
 {
-	struct virtnet_info *vi = rq->vq->vdev->priv;
-	struct virtnet_rq_stats stats = {};
 	unsigned int len;
 	int packets = 0;
 	void *buf;
-	int i;
 
 	if (!vi->big_packets || 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);
+			receive_buf(vi, rq, buf, len, ctx, xdp_xmit, stats);
 			packets++;
 		}
 	} else {
 		while (packets < budget &&
 		       (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
-			receive_buf(vi, rq, buf, len, NULL, xdp_xmit, &stats);
+			receive_buf(vi, rq, buf, len, NULL, xdp_xmit, stats);
 			packets++;
 		}
 	}
 
+	return packets;
+}
+
+static int virtnet_receive(struct receive_queue *rq, int budget,
+			   unsigned int *xdp_xmit)
+{
+	struct virtnet_info *vi = rq->vq->vdev->priv;
+	struct virtnet_rq_stats stats = {};
+	int i, packets;
+
+	if (rq->xsk_pool)
+		packets = virtnet_receive_xsk_bufs(vi, rq, budget, xdp_xmit, &stats);
+	else
+		packets = virtnet_receive_packets(vi, rq, budget, xdp_xmit, &stats);
+
 	if (rq->vq->num_free > min((unsigned int)budget, virtqueue_get_vring_size(rq->vq)) / 2) {
 		if (!try_fill_recv(vi, rq, GFP_ATOMIC)) {
 			spin_lock(&vi->refill_lock);