Re: [PATCH bpf-next v5] virtio_net: add XDP meta data support

[Jason Wang <jasowang@redhat.com>]

On 2020/2/20 下午4:55, Yuya Kusakabe wrote:
> 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, where on program return with pass verdict, we call
> into skb_metadata_set().
>
> Tested with the script at
> https://github.com/higebu/virtio_net-xdp-metadata-test.
>
> Fixes: de8f3a83b0a0 ("bpf: add meta pointer for direct access")


I'm not sure this is correct since virtio-net claims to not support 
metadata by calling xdp_set_data_meta_invalid()?


> Signed-off-by: Yuya Kusakabe <yuya.kusakabe@gmail.com>
> ---
> v5:
>   - page_to_skb(): copy vnet header if hdr_valid without checking metasize.
>   - receive_small(): do not copy vnet header if xdp_prog is availavle.
>   - __virtnet_xdp_xmit_one(): remove the xdp_set_data_meta_invalid().
>   - improve comments.
> v4:
>   - improve commit message
> v3:
>   - fix preserve the vnet header in receive_small().
> v2:
>   - keep copy untouched in page_to_skb().
>   - preserve the vnet header in receive_small().
>   - fix indentation.
> ---
>   drivers/net/virtio_net.c | 54 ++++++++++++++++++++++++----------------
>   1 file changed, 33 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 2fe7a3188282..4ea0ae60c000 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;
> @@ -393,6 +393,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>   	else
>   		hdr_padded_len = sizeof(struct padded_vnet_hdr);
>   
> +	/* hdr_valid means no XDP, so we can copy the vnet header */
>   	if (hdr_valid)
>   		memcpy(hdr, p, hdr_len);
>   
> @@ -405,6 +406,11 @@ 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;
>   
> @@ -450,10 +456,6 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>   	struct virtio_net_hdr_mrg_rxbuf *hdr;
>   	int err;
>   
> -	/* virtqueue want to use data area in-front of packet */
> -	if (unlikely(xdpf->metasize > 0))
> -		return -EOPNOTSUPP;
> -
>   	if (unlikely(xdpf->headroom < vi->hdr_len))
>   		return -EOVERFLOW;
>   
> @@ -644,6 +646,7 @@ 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;
> @@ -683,8 +686,8 @@ 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;
>   		act = bpf_prog_run_xdp(xdp_prog, &xdp);
> @@ -695,6 +698,7 @@ 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++;
> @@ -735,11 +739,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
>   	}
>   	skb_reserve(skb, headroom - delta);
>   	skb_put(skb, len);
> -	if (!delta) {
> +	if (!xdp_prog) {
>   		buf += header_offset;
>   		memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
>   	} /* keep zeroed vnet hdr since packet was changed by bpf */


I prefer to make this an independent patch and cc stable.

Other looks good.

Thanks


>   
> +	if (metasize)
> +		skb_metadata_set(skb, metasize);
> +
>   err:
>   	return skb;
>   
> @@ -760,8 +767,8 @@ 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 +800,7 @@ 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 +847,8 @@ 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);
> @@ -848,24 +856,27 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>   
>   		switch (act) {
>   		case XDP_PASS:
> +			metasize = xdp.data - xdp.data_meta;
> +
>   			/* recalculate offset to account for any header
> -			 * adjustments. Note other cases do not build an
> -			 * skb and avoid using offset
> +			 * adjustments and minus the metasize to copy the
> +			 * metadata in page_to_skb(). Note other cases do not
> +			 * build an skb and avoid using offset
>   			 */
> -			offset = xdp.data -
> -					page_address(xdp_page) - vi->hdr_len;
> +			offset = xdp.data - page_address(xdp_page) -
> +				 vi->hdr_len - metasize;
>   
> -			/* recalculate len if xdp.data or xdp.data_end were
> -			 * adjusted
> +			/* recalculate len if xdp.data, xdp.data_end or
> +			 * xdp.data_meta were adjusted
>   			 */
> -			len = xdp.data_end - xdp.data + vi->hdr_len;
> +			len = xdp.data_end - xdp.data + vi->hdr_len + metasize;
>   			/* We can only create skb based on xdp_page. */
>   			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;
> @@ -921,7 +932,8 @@ 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))