Re: [PATCH v8 bpf-next 03/14] net: mvneta: update mb bit before passing the xdp buffer to eBPF layer

[Vladimir Oltean <olteanv@gmail.com>]

On Thu, Apr 08, 2021 at 02:50:55PM +0200, Lorenzo Bianconi wrote:
> Update multi-buffer bit (mb) in xdp_buff to notify XDP/eBPF layer and
> XDP remote drivers if this is a "non-linear" XDP buffer. Access
> xdp_shared_info only if xdp_buff mb is set.
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> ---
>  drivers/net/ethernet/marvell/mvneta.c | 26 ++++++++++++++++++++------
>  1 file changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index a52e132fd2cf..94e29cce693a 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -2041,12 +2041,16 @@ mvneta_xdp_put_buff(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
>  {
>  	int i;
>  
> +	if (likely(!xdp->mb))
> +		goto out;
> +

Is there any particular reason for this extra check?

>  	for (i = 0; i < xdp_sinfo->nr_frags; i++) {
>  		skb_frag_t *frag = &xdp_sinfo->frags[i];
>  
>  		page_pool_put_full_page(rxq->page_pool,
>  					xdp_get_frag_page(frag), true);
>  	}
> +out:
>  	page_pool_put_page(rxq->page_pool, virt_to_head_page(xdp->data),
>  			   sync_len, true);
>  }
> @@ -2246,7 +2250,6 @@ mvneta_swbm_rx_frame(struct mvneta_port *pp,
>  {
>  	unsigned char *data = page_address(page);
>  	int data_len = -MVNETA_MH_SIZE, len;
> -	struct xdp_shared_info *xdp_sinfo;
>  	struct net_device *dev = pp->dev;
>  	enum dma_data_direction dma_dir;
>  
> @@ -2270,9 +2273,6 @@ mvneta_swbm_rx_frame(struct mvneta_port *pp,
>  	prefetch(data);
>  	xdp_prepare_buff(xdp, data, pp->rx_offset_correction + MVNETA_MH_SIZE,
>  			 data_len, false);
> -
> -	xdp_sinfo = xdp_get_shared_info_from_buff(xdp);
> -	xdp_sinfo->nr_frags = 0;
>  }
>  
>  static void
> @@ -2307,12 +2307,18 @@ mvneta_swbm_add_rx_fragment(struct mvneta_port *pp,
>  		xdp_set_frag_size(frag, data_len);
>  		xdp_set_frag_page(frag, page);
>  
> +		if (!xdp->mb) {
> +			xdp_sinfo->data_length = *size;
> +			xdp->mb = 1;
> +		}
>  		/* last fragment */
>  		if (len == *size) {
>  			struct xdp_shared_info *sinfo;
>  
>  			sinfo = xdp_get_shared_info_from_buff(xdp);
>  			sinfo->nr_frags = xdp_sinfo->nr_frags;
> +			sinfo->data_length = xdp_sinfo->data_length;
> +
>  			memcpy(sinfo->frags, xdp_sinfo->frags,
>  			       sinfo->nr_frags * sizeof(skb_frag_t));
>  		}
> @@ -2327,11 +2333,15 @@ mvneta_swbm_build_skb(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
>  		      struct xdp_buff *xdp, u32 desc_status)
>  {
>  	struct xdp_shared_info *xdp_sinfo = xdp_get_shared_info_from_buff(xdp);
> -	int i, num_frags = xdp_sinfo->nr_frags;
>  	skb_frag_t frag_list[MAX_SKB_FRAGS];
> +	int i, num_frags = 0;
>  	struct sk_buff *skb;
>  
> -	memcpy(frag_list, xdp_sinfo->frags, sizeof(skb_frag_t) * num_frags);
> +	if (unlikely(xdp->mb)) {
> +		num_frags = xdp_sinfo->nr_frags;
> +		memcpy(frag_list, xdp_sinfo->frags,
> +		       sizeof(skb_frag_t) * num_frags);
> +	}
>  
>  	skb = build_skb(xdp->data_hard_start, PAGE_SIZE);
>  	if (!skb)
> @@ -2343,6 +2353,9 @@ mvneta_swbm_build_skb(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
>  	skb_put(skb, xdp->data_end - xdp->data);
>  	mvneta_rx_csum(pp, desc_status, skb);
>  
> +	if (likely(!xdp->mb))
> +		return skb;
> +
>  	for (i = 0; i < num_frags; i++) {
>  		struct page *page = xdp_get_frag_page(&frag_list[i]);
>  
> @@ -2404,6 +2417,7 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
>  			frame_sz = size - ETH_FCS_LEN;
>  			desc_status = rx_status;
>  
> +			xdp_buf.mb = 0;
>  			mvneta_swbm_rx_frame(pp, rx_desc, rxq, &xdp_buf,
>  					     &size, page);
>  		} else {
> -- 
> 2.30.2
>