Re: [PATCH bpf-next v4] virtio_net: add XDP meta data support

Implement support for transferring XDP meta data into skb for
virtio_net driver; before calling into the program, xdp.data_meta points
to xdp.data and copy vnet header to the front of xdp.data_hard_start
to avoid overwriting it, where on program return with pass verdict,
we call into skb_metadata_set().

Fixes: de8f3a83b0a0 ("bpf: add meta pointer for direct access")
Signed-off-by: Yuya Kusakabe <redacted>
---
  drivers/net/virtio_net.c | 47 ++++++++++++++++++++++++++++------------
  1 file changed, 33 insertions(+), 14 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 2fe7a3188282..5fdd6ea0e3f1 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -371,7 +371,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
  				   struct receive_queue *rq,
  				   struct page *page, unsigned int offset,
  				   unsigned int len, unsigned int truesize,
-				   bool hdr_valid)
+				   bool hdr_valid, unsigned int metasize)
  {
  	struct sk_buff *skb;
  	struct virtio_net_hdr_mrg_rxbuf *hdr;

@@ -393,7 +393,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
  	else
  		hdr_padded_len = sizeof(struct padded_vnet_hdr);
  
-	if (hdr_valid)
+	if (hdr_valid && !metasize)

  		memcpy(hdr, p, hdr_len);
  
  	len -= hdr_len;

@@ -405,6 +405,11 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
  		copy = skb_tailroom(skb);
  	skb_put_data(skb, p, copy);
  
+	if (metasize) {
+		__skb_pull(skb, metasize);
+		skb_metadata_set(skb, metasize);
+	}
+
  	len -= copy;
  	offset += copy;
  

@@ -644,6 +649,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
  	unsigned int delta = 0;
  	struct page *xdp_page;
  	int err;
+	unsigned int metasize = 0;
  
  	len -= vi->hdr_len;
  	stats->bytes += len;

@@ -683,10 +689,15 @@ static struct sk_buff *receive_small(struct net_device *dev,
  
  		xdp.data_hard_start = buf + VIRTNET_RX_PAD + vi->hdr_len;
  		xdp.data = xdp.data_hard_start + xdp_headroom;
-		xdp_set_data_meta_invalid(&xdp);
  		xdp.data_end = xdp.data + len;
+		xdp.data_meta = xdp.data;
  		xdp.rxq = &rq->xdp_rxq;
  		orig_data = xdp.data;
+		/* Copy the vnet header to the front of data_hard_start to avoid
+		 * overwriting it by XDP meta data.
+		 */
+		memcpy(xdp.data_hard_start - vi->hdr_len,
+		       xdp.data - vi->hdr_len, vi->hdr_len);

  		act = bpf_prog_run_xdp(xdp_prog, &xdp);
  		stats->xdp_packets++;
  

@@ -695,9 +706,11 @@ static struct sk_buff *receive_small(struct net_device *dev,
  			/* Recalculate length in case bpf program changed it */
  			delta = orig_data - xdp.data;
  			len = xdp.data_end - xdp.data;
+			metasize = xdp.data - xdp.data_meta;
  			break;
  		case XDP_TX:
  			stats->xdp_tx++;
+			xdp.data_meta = xdp.data;

  			xdpf = convert_to_xdp_frame(&xdp);
  			if (unlikely(!xdpf))
  				goto err_xdp;

@@ -736,10 +749,12 @@ static struct sk_buff *receive_small(struct net_device *dev,
  	skb_reserve(skb, headroom - delta);
  	skb_put(skb, len);
  	if (!delta) {

-		buf += header_offset;
-		memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
+		memcpy(skb_vnet_hdr(skb), buf + VIRTNET_RX_PAD, vi->hdr_len);
  	} /* keep zeroed vnet hdr since packet was changed by bpf */
  
+	if (metasize)
+		skb_metadata_set(skb, metasize);
+
  err:
  	return skb;
  

@@ -760,8 +775,8 @@ static struct sk_buff *receive_big(struct net_device *dev,
  				   struct virtnet_rq_stats *stats)
  {
  	struct page *page = buf;
-	struct sk_buff *skb = page_to_skb(vi, rq, page, 0, len,
-					  PAGE_SIZE, true);
+	struct sk_buff *skb =
+		page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, true, 0);
  
  	stats->bytes += len - vi->hdr_len;
  	if (unlikely(!skb))

@@ -793,6 +808,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
  	unsigned int truesize;
  	unsigned int headroom = mergeable_ctx_to_headroom(ctx);
  	int err;
+	unsigned int metasize = 0;
  
  	head_skb = NULL;
  	stats->bytes += len - vi->hdr_len;

@@ -839,8 +855,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
  		data = page_address(xdp_page) + offset;
  		xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM + vi->hdr_len;
  		xdp.data = data + vi->hdr_len;
-		xdp_set_data_meta_invalid(&xdp);
  		xdp.data_end = xdp.data + (len - vi->hdr_len);
+		xdp.data_meta = xdp.data;
  		xdp.rxq = &rq->xdp_rxq;
  
  		act = bpf_prog_run_xdp(xdp_prog, &xdp);

@@ -852,8 +868,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
  			 * adjustments. Note other cases do not build an
  			 * skb and avoid using offset
  			 */
-			offset = xdp.data -
-					page_address(xdp_page) - vi->hdr_len;
+			metasize = xdp.data - xdp.data_meta;
+			offset = xdp.data - page_address(xdp_page) -
+				 vi->hdr_len - metasize;
  
  			/* recalculate len if xdp.data or xdp.data_end were
  			 * adjusted

@@ -863,14 +880,15 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
  			if (unlikely(xdp_page != page)) {
  				rcu_read_unlock();
  				put_page(page);
-				head_skb = page_to_skb(vi, rq, xdp_page,
-						       offset, len,
-						       PAGE_SIZE, false);
+				head_skb = page_to_skb(vi, rq, xdp_page, offset,
+						       len, PAGE_SIZE, false,
+						       metasize);
  				return head_skb;
  			}
  			break;
  		case XDP_TX:
  			stats->xdp_tx++;
+			xdp.data_meta = xdp.data;

  			xdpf = convert_to_xdp_frame(&xdp);
  			if (unlikely(!xdpf))
  				goto err_xdp;

@@ -921,7 +939,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
  		goto err_skb;
  	}
  
-	head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog);
+	head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog,
+			       metasize);
  	curr_skb = head_skb;
  
  	if (unlikely(!curr_skb))