From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5383B7E1; Thu, 30 Nov 2023 10:51:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="I9VUdcHo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 42D82C433C8; Thu, 30 Nov 2023 10:51:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1701341468; bh=C5kbXo/gctXjAbzU0h/Mx0eFgqpdb3BArHPQBNYJcRg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=I9VUdcHoFH4AY0XC7+sC4TWxIPLEaT5ev4M9japNPVVLIAcQ3gqd+vYBnS9Yuq6Vc AUVOm0LbIemdSbxMRmjgMjcSmLhR8PsKVhXA4rjhR7EU0Q8jr20F/9Xo+We6u14jdw 7yBacNtg4Tf7ckx4eN403woWVupBxSM/oN2AS4x2etYe779G1Hs3cGkgPS9VHh2HK8 BDhZTniEaoYh2AlFsOzsguyi2jOl6wWch/wAeHC5TK14KKgVCPFLyY7//h4xeQfxbt 2lr0jazPDrU+PgqV+tJHibXFVeMhqozZrFAboPtbyBzgZtg/uqIByaCLeWpl5v6n4i egpb+h1LrmiXw== Date: Thu, 30 Nov 2023 11:51:05 +0100 From: Lorenzo Bianconi To: Jesper Dangaard Brouer Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, lorenzo.bianconi@redhat.com, bpf@vger.kernel.org, toke@redhat.com, willemdebruijn.kernel@gmail.com, jasowang@redhat.com, kernel-team , Yan Zhai Subject: Re: [PATCH v2 net-next 2/2] xdp: add multi-buff support for xdp running in generic mode Message-ID: References: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="xJ4yJrSLfRCBhu4w" Content-Disposition: inline In-Reply-To: --xJ4yJrSLfRCBhu4w Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable >=20 >=20 > 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. > >=20 > > Signed-off-by: Lorenzo Bianconi > > --- > > net/core/dev.c | 144 ++++++++++++++++++++++++++++++++++++++++--------- > > 1 file changed, 119 insertions(+), 25 deletions(-) > >=20 > > 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 =3D skb->data_len; > > + xdp_buff_set_frags_flag(xdp); > > + } else { > > + xdp_buff_clear_frags_flag(xdp); > > + } > > orig_data_end =3D xdp->data_end; > > orig_data =3D xdp->data; > > @@ -4882,6 +4888,14 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb= , struct xdp_buff *xdp, > > skb->len +=3D 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 =3D skb_shinfo(skb)->xdp_frags_size; > > + else > > + skb->data_len =3D 0; > > + > > /* check if XDP changed eth hdr such SKB needs update */ > > eth =3D (struct ethhdr *)xdp->data; > > if ((orig_eth_type !=3D eth->h_proto) || > > @@ -4915,54 +4929,134 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *s= kb, 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) >=20 > I like this is split out into a check function. >=20 > > { > > struct sk_buff *skb =3D *pskb; > > - u32 act =3D XDP_DROP; > > - > > - /* Reinjected packets coming from act_mirred or similar should > > - * not get XDP generic processing. > > - */ > > - if (skb_is_redirected(skb)) > > - return XDP_PASS; >=20 > (For other reviewers) > This reinjected check is moved further down. >=20 > > + 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 =3D XDP_PACKET_HEADROOM - skb_headroom(skb); > > int troom =3D 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 =3D pskb_expand_head(skb, > > + hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0, > > + troom > 0 ? troom + 128 : 0, GFP_ATOMIC); > > + if (err) > > + return err; > > + > > + err =3D 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 || >=20 > 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@kernel.org/ >=20 > So check would be: (skb_cloned(skb) || skb_shared(skb) ||) >=20 > > + skb_headroom(skb) < XDP_PACKET_HEADROOM) { >=20 > [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. >=20 > [4/4] https://lore.kernel.org/netdev/169272716651.1975370.105147112338782= 78884.stgit@firesoul/ Ah nice, for some reason I missed this patch >=20 >=20 >=20 > > + u32 mac_len =3D 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 =3D SKB_WITH_OVERHEAD(PAGE_SIZE - > > + XDP_PACKET_HEADROOM); > > + if (skb->len > max_head_size + MAX_SKB_FRAGS * PAGE_SIZE) > > + return -ENOMEM; > > + > > + size =3D min_t(u32, skb->len, max_head_size); > > + nskb =3D netdev_alloc_skb(skb->dev, size + XDP_PACKET_HEADROOM); >=20 >=20 > Would is be possible to use napi_alloc_skb() here? >=20 > 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 >=20 >=20 > > + if (!nskb) > > + return -ENOMEM; > > + > > + skb_reserve(nskb, XDP_PACKET_HEADROOM); > > + skb_copy_header(nskb, skb); > > + > > + err =3D skb_copy_bits(skb, 0, nskb->data, size); > > + if (err) { > > + consume_skb(nskb); > > + return err; > > + } > > + skb_put(nskb, size); > > + > > + head_off =3D skb_headroom(nskb) - skb_headroom(skb); > > + skb_headers_offset_update(nskb, head_off); > > + > > + off =3D size; > > + len =3D skb->len - off; > > + for (i =3D 0; i < MAX_SKB_FRAGS && off < skb->len; i++) { > > + struct page *page; > > + void *frag; > > + > > + size =3D min_t(u32, len, PAGE_SIZE); > > + frag =3D netdev_alloc_frag(size); >=20 > Again the slower variant. >=20 > > + if (!frag) { > > + consume_skb(nskb); > > + return -ENOMEM; > > + } > > + > > + page =3D virt_to_head_page(frag); > > + skb_add_rx_frag(nskb, i, page, > > + frag - page_address(page), size, size); > > + err =3D skb_copy_bits(skb, off, frag, size); > > + if (err) { > > + consume_skb(nskb); > > + return err; > > + } > > + > > + len -=3D size; > > + off +=3D size; > > + } > > + > > + consume_skb(skb); > > + *pskb =3D nskb; > > + __skb_pull(nskb, mac_len); > > } > > - act =3D 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 =3D 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 =3D 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; > > } >=20 > Overall I like the patch :-) >=20 > Are we missing more things to allow GRO packets getting processed by gene= ric > XDP? >=20 > --Jesper --xJ4yJrSLfRCBhu4w Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTquNwa3Txd3rGGn7Y6cBh0uS2trAUCZWhpGQAKCRA6cBh0uS2t rNSXAPkBbXXtyondlxXatKSCQ1Q4FHmYZpEX3qhUQa0g6uf1TwD/RxipW7a3poGE InG6F5JCmDWSt3aPSB8/Y6qJuC+6CAo= =hxOB -----END PGP SIGNATURE----- --xJ4yJrSLfRCBhu4w--