From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F028FC43381 for ; Thu, 14 Feb 2019 04:39:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AC775222B6 for ; Thu, 14 Feb 2019 04:39:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="T6U4oAj9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390582AbfBNEjh (ORCPT ); Wed, 13 Feb 2019 23:39:37 -0500 Received: from mail-pl1-f196.google.com ([209.85.214.196]:46819 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388956AbfBNEjg (ORCPT ); Wed, 13 Feb 2019 23:39:36 -0500 Received: by mail-pl1-f196.google.com with SMTP id o6so2427488pls.13 for ; Wed, 13 Feb 2019 20:39:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=KfTxAjkTdPnr9xnr8W/lDH1wNMV/m63Rhfm1kFNAilA=; b=T6U4oAj9A9Td5M5CGaSdn0lTG7z+EvTT6lMkL1TaVFyQ09DlYiSjMzQlCrxxPnbVPK Mfb81mBqMeeSrcQufdVM4VfTEcKHUA7cXCtWa+Hnv7bUmCmO+/cD4bgA+FNTIBtx8k2a ELdUJA0qr2sdqR0M5kMeu8Rm2DRXXMy3JAdBi2jgtS5GvY4HtKDh1/f6or2/Jn0cgA10 qvJVCVuqhBH8nmTayXfwI63e6MOvz3uHOxlvfjm29OkapNgxmn6D0iS++WpP493RLS2J /Y+kARyOnSJmM5oomBaTLImTvMs/bF47D436PakisD5DF27lqk9fE8iiQP/PwAZk+2MF sr+w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=KfTxAjkTdPnr9xnr8W/lDH1wNMV/m63Rhfm1kFNAilA=; b=RyQoj3wLcPPcMHmvvUPyAIU0KeOsKdtxQiFEnUrVTjgwEkK8WEnx4CqzbDU7BqmCal gUKgAh4Oqkk2tabimYGli98JitJFEULE6AQTEncdrBSsyi4ZrUI6ABELb2+BE6UL4Nar zmeS45CltSZYJkVoET+IPe+6bj3M1Ty85hzZXzrfQaHjKsYWD9a7ay4rK8WbIHAs3ujh eQIN/vRGIHoUzmRIp67viFoCKGQtz+dY9uI5aK0mePY1lWmgYCS0xB/b1jok05tsdGxG zvoOamYrlW3kHxJgz24il1o5fE32fpXfHP44xaCXLmJsGbijU1dyrlaSPcM0aA0xs1kR dXXA== X-Gm-Message-State: AHQUAuaZRqbcA2ngMXcChQZseZxdAGjaSq2jlkbtw9jxRPYrqphmiKa0 N+8fHGzWQcu4veQMcKxrST4= X-Google-Smtp-Source: AHgI3IYtyZS2Ns/C6Dk8lAve58/djjA48EOLHwVQncuiLu+Kj3r88RcUEKNt3gmvrCDDR+lSr4spzw== X-Received: by 2002:a17:902:129:: with SMTP id 38mr2105354plb.140.1550119175834; Wed, 13 Feb 2019 20:39:35 -0800 (PST) Received: from ast-mbp ([2620:10d:c090:180::1:1fdb]) by smtp.gmail.com with ESMTPSA id l19sm1358183pfi.71.2019.02.13.20.39.34 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 13 Feb 2019 20:39:34 -0800 (PST) Date: Wed, 13 Feb 2019 20:39:32 -0800 From: Alexei Starovoitov To: Stanislav Fomichev Cc: Willem de Bruijn , Stanislav Fomichev , Network Development , David Miller , Alexei Starovoitov , Daniel Borkmann , simon.horman@netronome.com, Willem de Bruijn Subject: Re: [RFC bpf-next 0/7] net: flow_dissector: trigger BPF hook when called from eth_get_headlen Message-ID: <20190214043931.hdpddeom57rnnlhm@ast-mbp> References: <20190205173629.160717-1-sdf@google.com> <20190205204003.GB10769@mini-arch> <20190206004714.pz44evow5uwgvt4x@ast-mbp.dhcp.thefacebook.com> <20190206005931.GF10769@mini-arch> <20190206031215.qldeh7pfgqr3frg3@ast-mbp> <20190206035619.GG10769@mini-arch> <20190206041112.h3ccahimp2uerdfk@ast-mbp> <20190206054946.GH10769@mini-arch> <20190212170232.GB10595@mini-arch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190212170232.GB10595@mini-arch> User-Agent: NeoMutt/20180223 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Feb 12, 2019 at 09:02:32AM -0800, Stanislav Fomichev wrote: > On 02/05, Stanislav Fomichev wrote: > > On 02/05, Alexei Starovoitov wrote: > > > On Tue, Feb 05, 2019 at 07:56:19PM -0800, Stanislav Fomichev wrote: > > > > On 02/05, Alexei Starovoitov wrote: > > > > > On Tue, Feb 05, 2019 at 04:59:31PM -0800, Stanislav Fomichev wrote: > > > > > > On 02/05, Alexei Starovoitov wrote: > > > > > > > On Tue, Feb 05, 2019 at 12:40:03PM -0800, Stanislav Fomichev wrote: > > > > > > > > On 02/05, Willem de Bruijn wrote: > > > > > > > > > On Tue, Feb 5, 2019 at 12:57 PM Stanislav Fomichev wrote: > > > > > > > > > > > > > > > > > > > > Currently, when eth_get_headlen calls flow dissector, it doesn't pass any > > > > > > > > > > skb. Because we use passed skb to lookup associated networking namespace > > > > > > > > > > to find whether we have a BPF program attached or not, we always use > > > > > > > > > > C-based flow dissector in this case. > > > > > > > > > > > > > > > > > > > > The goal of this patch series is to add new networking namespace argument > > > > > > > > > > to the eth_get_headlen and make BPF flow dissector programs be able to > > > > > > > > > > work in the skb-less case. > > > > > > > > > > > > > > > > > > > > The series goes like this: > > > > > > > > > > 1. introduce __init_skb and __init_skb_shinfo; those will be used to > > > > > > > > > > initialize temporary skb > > > > > > > > > > 2. introduce skb_net which can be used to get networking namespace > > > > > > > > > > associated with an skb > > > > > > > > > > 3. add new optional network namespace argument to __skb_flow_dissect and > > > > > > > > > > plumb through the callers > > > > > > > > > > 4. add new __flow_bpf_dissect which constructs temporary on-stack skb > > > > > > > > > > (using __init_skb) and calls BPF flow dissector program > > > > > > > > > > > > > > > > > > The main concern I see with this series is this cost of skb zeroing > > > > > > > > > for every packet in the device driver receive routine, *independent* > > > > > > > > > from the real skb allocation and zeroing which will likely happen > > > > > > > > > later. > > > > > > > > Yes, plus ~200 bytes on the stack for the callers. > > > > > > > > > > > > > > > > Not sure how visible this zeroing though, I can probably try to get some > > > > > > > > numbers from BPF_PROG_TEST_RUN (running current version vs running with > > > > > > > > on-stack skb). > > > > > > > > > > > > > > imo extra 256 byte memset for every packet is non starter. > > > > > > We can put pre-allocated/initialized skbs without data into percpu or even > > > > > > use pcpu_freelist_pop/pcpu_freelist_push to make sure we don't have to think > > > > > > about having multiple percpu for irq/softirq/process contexts. > > > > > > Any concerns with that approach? > > > > > > Any other possible concerns with the overall series? > > > > > > > > > > I'm missing why the whole thing is needed. > > > > > You're saying: > > > > > " make BPF flow dissector programs be able to work in the skb-less case". > > > > > What does it mean specifically? > > > > > The only non-skb case is XDP. > > > > > Are you saying you want flow_dissector prog to be run in XDP? > > > > eth_get_headlen that drivers call on RX path on a chunk of data to > > > > guesstimate the length of the headers calls flow dissector without an skb > > > > (__skb_flow_dissect was a weird interface where it accepts skb or > > > > data+len). Right now, there is no way to trigger BPF flow dissector > > > > for this case (we don't have an skb to get associated namespace/etc/etc). > > > > The patch series tries to fix that to make sure that we always trigger > > > > BPF program if it's attached to a device's namespace. > > > > > > then why not to create flow_dissector prog type that works without skb? > > > Why do you need to fake an skb? > > > XDP progs work just fine without it. > > What's the advantage of having another prog type? In this case we would have > > to write the same flow dissector program twice: first time against __skb_buff > > interface, second time against xdp_md. > > By using fake skb, we make the same flow dissector __sk_buff BPF program > > work in both contexts without a rewrite to an xdp interface (I don't > > think users should care whether flow dissector was called form "xdp" vs skb > > context; and we're sort of stuck with __sk_buff interface already). > Should I follow up with v2 where I address memset(,,256) for each packet? > Or you still have some questions/doubts/suggestions regarding the problem > I'm trying to solve? sorry for delay. I'm still thinking what is the path forward here. That 'stuck with __sk_buff' is what bothers me. It's an indication that api wasn't thought through if first thing it needs is this fake skb hack. If bpf_flow.c is a realistic example of such flow dissector prog it means that real skb fields are accessed. In particular skb->vlan_proto, skb->protocol. These fields in case of 'fake skb' will not be set, since eth_type_trans() isn't called yet. So either flow_dissector needs a real __sk_buff and all of its fields should be real or it's a different flow_dissector prog type that needs ctx->data, ctx->data_end, ctx->flow_keys only. Either way going with fake skb is incorrect, since bpf_flow.c example will be broken and for program writers it will be hard to figure why it's broken.