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

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Message-ID: <YHB/078gnE/wcvNw@lore-desk>
Date:   Fri, 9 Apr 2021 18:24:51 +0200
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        lorenzo.bianconi@...hat.com, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, shayagr@...zon.com,
        sameehj@...zon.com, john.fastabend@...il.com, dsahern@...nel.org,
        brouer@...hat.com, echaudro@...hat.com, jasowang@...hat.com,
        alexander.duyck@...il.com, saeed@...nel.org,
        maciej.fijalkowski@...el.com
Subject: Re: [PATCH v8 bpf-next 03/14] net: mvneta: update mb bit before
 passing the xdp buffer to eBPF layer

> 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@...nel.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?

xdp_sinfo->frags[] is initialized just if xdp->mb is set.

Regards,
Lorenzo

> 
> >  	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
> > 
> 

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