> > > On 11/30/23 10:11, Lorenzo Bianconi wrote: > > Similar to native xdp, do not always linearize the skb in > > netif_receive_generic_xdp routine but create a non-linear xdp_buff to be > > processed by the eBPF program. This allow to add multi-buffer support > > for xdp running in generic mode. > > > > Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx> > > --- > > net/core/dev.c | 144 ++++++++++++++++++++++++++++++++++++++++--------- > > 1 file changed, 119 insertions(+), 25 deletions(-) > > > > diff --git a/net/core/dev.c b/net/core/dev.c > > index 4df68d7f04a2..0d08e755bb7f 100644 > > --- a/net/core/dev.c > > +++ b/net/core/dev.c > > @@ -4853,6 +4853,12 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp, > > xdp_init_buff(xdp, frame_sz, &rxqueue->xdp_rxq); > > xdp_prepare_buff(xdp, hard_start, skb_headroom(skb) - mac_len, > > skb_headlen(skb) + mac_len, true); > > + if (skb_is_nonlinear(skb)) { > > + skb_shinfo(skb)->xdp_frags_size = skb->data_len; > > + xdp_buff_set_frags_flag(xdp); > > + } else { > > + xdp_buff_clear_frags_flag(xdp); > > + } > > orig_data_end = xdp->data_end; > > orig_data = xdp->data; > > @@ -4882,6 +4888,14 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp, > > skb->len += off; /* positive on grow, negative on shrink */ > > } > > + /* XDP frag metadata (e.g. nr_frags) are updated in eBPF helpers > > + * (e.g. bpf_xdp_adjust_tail), we need to update data_len here. > > + */ > > + if (xdp_buff_has_frags(xdp)) > > + skb->data_len = skb_shinfo(skb)->xdp_frags_size; > > + else > > + skb->data_len = 0; > > + > > /* check if XDP changed eth hdr such SKB needs update */ > > eth = (struct ethhdr *)xdp->data; > > if ((orig_eth_type != eth->h_proto) || > > @@ -4915,54 +4929,134 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp, > > return act; > > } > > -static u32 netif_receive_generic_xdp(struct sk_buff **pskb, > > - struct xdp_buff *xdp, > > - struct bpf_prog *xdp_prog) > > +static int netif_skb_check_for_generic_xdp(struct sk_buff **pskb, > > + struct bpf_prog *prog) > > I like this is split out into a check function. > > > { > > struct sk_buff *skb = *pskb; > > - u32 act = XDP_DROP; > > - > > - /* Reinjected packets coming from act_mirred or similar should > > - * not get XDP generic processing. > > - */ > > - if (skb_is_redirected(skb)) > > - return XDP_PASS; > > (For other reviewers) > This reinjected check is moved further down. > > > + int err; > > - /* XDP packets must be linear and must have sufficient headroom > > - * of XDP_PACKET_HEADROOM bytes. This is the guarantee that also > > - * native XDP provides, thus we need to do it here as well. > > + /* XDP does not support fraglist so we need to linearize > > + * the skb. > > */ > > - if (skb_cloned(skb) || skb_is_nonlinear(skb) || > > - skb_headroom(skb) < XDP_PACKET_HEADROOM) { > > + if (skb_has_frag_list(skb) || !prog->aux->xdp_has_frags) { > > int hroom = XDP_PACKET_HEADROOM - skb_headroom(skb); > > int troom = skb->tail + skb->data_len - skb->end; > > /* In case we have to go down the path and also linearize, > > * then lets do the pskb_expand_head() work just once here. > > */ > > - if (pskb_expand_head(skb, > > - hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0, > > - troom > 0 ? troom + 128 : 0, GFP_ATOMIC)) > > - goto do_drop; > > - if (skb_linearize(skb)) > > - goto do_drop; > > + err = pskb_expand_head(skb, > > + hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0, > > + troom > 0 ? troom + 128 : 0, GFP_ATOMIC); > > + if (err) > > + return err; > > + > > + err = skb_linearize(skb); > > + if (err) > > + return err; > > + > > + return 0; > > + } > > + > > + /* XDP packets must have sufficient headroom of XDP_PACKET_HEADROOM > > + * bytes. This is the guarantee that also native XDP provides, > > + * thus we need to do it here as well. > > + */ > > + if (skb_cloned(skb) || skb_shinfo(skb)->nr_frags || > > I though we could allow a SKB with skb_shinfo(skb)->nr_frags (that isn't > cloned or shared) to be processed by generic XDP without any reallocation? I do not think so, we discussed about it with Jakub here [0] [0] https://lore.kernel.org/netdev/20231128105145.7b39db7d@xxxxxxxxxx/ > > So check would be: (skb_cloned(skb) || skb_shared(skb) ||) > > > + skb_headroom(skb) < XDP_PACKET_HEADROOM) { > > [Headroom trick] > For layered devices the netstack could be the process that created the > SKB. If you noticed my veth patchset[4/4], when I detect an XDP-prog > attach, I'm increasing the net_device headroom (.ndo_set_rx_headroom) > such that netstack will allocated enough headroom to satisfy > XDP_PACKET_HEADROOM. > > [4/4] https://lore.kernel.org/netdev/169272716651.1975370.10514711233878278884.stgit@firesoul/ Ah nice, for some reason I missed this patch > > > > > + u32 mac_len = skb->data - skb_mac_header(skb); > > + u32 size, len, max_head_size, off; > > + struct sk_buff *nskb; > > + int i, head_off; > > + > > + __skb_push(skb, mac_len); > > + max_head_size = SKB_WITH_OVERHEAD(PAGE_SIZE - > > + XDP_PACKET_HEADROOM); > > + if (skb->len > max_head_size + MAX_SKB_FRAGS * PAGE_SIZE) > > + return -ENOMEM; > > + > > + size = min_t(u32, skb->len, max_head_size); > > + nskb = netdev_alloc_skb(skb->dev, size + XDP_PACKET_HEADROOM); > > > Would is be possible to use napi_alloc_skb() here? > > The napi_alloc_skb() is faster than netdev_alloc_skb(), but it as name > suggest assumes this is called under NAPI protection/context. It > used-to-be the case for generic XDP, but code got moved around to > support layered devices, so I not 100% sure if this is always true (NAPI > context). Actually I was thinking about it and I was not 100% sure too (so I decided to use the non-NAPI version). Any input about it? Regards, Lorenzo > > > > + if (!nskb) > > + return -ENOMEM; > > + > > + skb_reserve(nskb, XDP_PACKET_HEADROOM); > > + skb_copy_header(nskb, skb); > > + > > + err = skb_copy_bits(skb, 0, nskb->data, size); > > + if (err) { > > + consume_skb(nskb); > > + return err; > > + } > > + skb_put(nskb, size); > > + > > + head_off = skb_headroom(nskb) - skb_headroom(skb); > > + skb_headers_offset_update(nskb, head_off); > > + > > + off = size; > > + len = skb->len - off; > > + for (i = 0; i < MAX_SKB_FRAGS && off < skb->len; i++) { > > + struct page *page; > > + void *frag; > > + > > + size = min_t(u32, len, PAGE_SIZE); > > + frag = netdev_alloc_frag(size); > > Again the slower variant. > > > + if (!frag) { > > + consume_skb(nskb); > > + return -ENOMEM; > > + } > > + > > + page = virt_to_head_page(frag); > > + skb_add_rx_frag(nskb, i, page, > > + frag - page_address(page), size, size); > > + err = skb_copy_bits(skb, off, frag, size); > > + if (err) { > > + consume_skb(nskb); > > + return err; > > + } > > + > > + len -= size; > > + off += size; > > + } > > + > > + consume_skb(skb); > > + *pskb = nskb; > > + __skb_pull(nskb, mac_len); > > } > > - act = bpf_prog_run_generic_xdp(skb, xdp, xdp_prog); > > + return 0; > > +} > > + > > +static u32 netif_receive_generic_xdp(struct sk_buff **pskb, > > + struct xdp_buff *xdp, > > + struct bpf_prog *xdp_prog) > > +{ > > + u32 act = XDP_DROP; > > + > > + /* Reinjected packets coming from act_mirred or similar should > > + * not get XDP generic processing. > > + */ > > + if (skb_is_redirected(*pskb)) > > + return XDP_PASS; > > + > > + if (netif_skb_check_for_generic_xdp(pskb, xdp_prog)) > > + goto do_drop; > > + > > + act = bpf_prog_run_generic_xdp(*pskb, xdp, xdp_prog); > > switch (act) { > > case XDP_REDIRECT: > > case XDP_TX: > > case XDP_PASS: > > break; > > default: > > - bpf_warn_invalid_xdp_action(skb->dev, xdp_prog, act); > > + bpf_warn_invalid_xdp_action((*pskb)->dev, xdp_prog, act); > > fallthrough; > > case XDP_ABORTED: > > - trace_xdp_exception(skb->dev, xdp_prog, act); > > + trace_xdp_exception((*pskb)->dev, xdp_prog, act); > > fallthrough; > > case XDP_DROP: > > do_drop: > > - kfree_skb(skb); > > + kfree_skb(*pskb); > > break; > > } > > Overall I like the patch :-) > > Are we missing more things to allow GRO packets getting processed by generic > XDP? > > --Jesper
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