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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 A9BD5C43603 for ; Fri, 20 Dec 2019 03:25:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5B40224680 for ; Fri, 20 Dec 2019 03:25:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hx8rO3n5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727179AbfLTDZG (ORCPT ); Thu, 19 Dec 2019 22:25:06 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:28965 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726964AbfLTDZG (ORCPT ); Thu, 19 Dec 2019 22:25:06 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1576812303; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=kGBsRXEKX2r9J8frnym0anFY1M8amTvC30ekMb58Nl4=; b=hx8rO3n5R7KBgXi0YSycClhuGL/wbXi/Z4Vc6mzMlCwUBC6vrSE52kvmvJ/sh53vp6FxXl BpHLW7raVbvc4QY7F8g6SnhbkZLkPtcuSZ2uAQghIC6ACoE9pIsccc2OkIz178hH47BJ/E WaSV4nZPBZ5EMANkEpE3A+vlHsObWzo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-416-GaefpPfiMQ6dN2kMFgRBgQ-1; Thu, 19 Dec 2019 22:25:01 -0500 X-MC-Unique: GaefpPfiMQ6dN2kMFgRBgQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3F8C3800D48; Fri, 20 Dec 2019 03:24:59 +0000 (UTC) Received: from [10.72.12.176] (ovpn-12-176.pek2.redhat.com [10.72.12.176]) by smtp.corp.redhat.com (Postfix) with ESMTP id 55C0B5D9E2; Fri, 20 Dec 2019 03:24:48 +0000 (UTC) Subject: Re: [RFC net-next 11/14] tun: run XDP program in tx path To: Prashant Bhole , =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= , Alexei Starovoitov , Jesper Dangaard Brouer Cc: "David S . Miller" , "Michael S . Tsirkin" , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , David Ahern , Jakub Kicinski , John Fastabend , Toshiaki Makita , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , netdev@vger.kernel.org, Ilias Apalodimas References: <20191218081050.10170-1-prashantbhole.linux@gmail.com> <20191218081050.10170-12-prashantbhole.linux@gmail.com> <20191218110732.33494957@carbon> <87fthh6ehg.fsf@toke.dk> <20191218181944.3ws2oy72hpyxshhb@ast-mbp.dhcp.thefacebook.com> <35a07230-3184-40bf-69ff-852bdfaf03c6@gmail.com> <874kxw4o4r.fsf@toke.dk> <5eb791bf-1876-0b4b-f721-cb3c607f846c@gmail.com> From: Jason Wang Message-ID: <75228f98-338e-453c-3ace-b6d36b26c51c@redhat.com> Date: Fri, 20 Dec 2019 11:24:47 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <5eb791bf-1876-0b4b-f721-cb3c607f846c@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Content-Transfer-Encoding: quoted-printable Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2019/12/20 =E4=B8=8A=E5=8D=888:07, Prashant Bhole wrote: > Note: Resending my last response. It was not delivered to netdev list > due to some problem. > > On 12/19/19 7:15 PM, Toke H=C3=B8iland-J=C3=B8rgensen wrote: >> Prashant Bhole writes: >> >>> On 12/19/19 3:19 AM, Alexei Starovoitov wrote: >>>> On Wed, Dec 18, 2019 at 12:48:59PM +0100, Toke H=C3=B8iland-J=C3=B8r= gensen=20 >>>> wrote: >>>>> Jesper Dangaard Brouer writes: >>>>> >>>>>> On Wed, 18 Dec 2019 17:10:47 +0900 >>>>>> Prashant Bhole wrote: >>>>>> >>>>>>> +static u32 tun_do_xdp_tx(struct tun_struct *tun, struct=20 >>>>>>> tun_file *tfile, >>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 struct xdp_frame *frame) >>>>>>> +{ >>>>>>> +=C2=A0=C2=A0=C2=A0 struct bpf_prog *xdp_prog; >>>>>>> +=C2=A0=C2=A0=C2=A0 struct tun_page tpage; >>>>>>> +=C2=A0=C2=A0=C2=A0 struct xdp_buff xdp; >>>>>>> +=C2=A0=C2=A0=C2=A0 u32 act =3D XDP_PASS; >>>>>>> +=C2=A0=C2=A0=C2=A0 int flush =3D 0; >>>>>>> + >>>>>>> +=C2=A0=C2=A0=C2=A0 xdp_prog =3D rcu_dereference(tun->xdp_tx_prog= ); >>>>>>> +=C2=A0=C2=A0=C2=A0 if (xdp_prog) { >>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 xdp.data_hard_start =3D= frame->data - frame->headroom; >>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 xdp.data =3D frame->d= ata; >>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 xdp.data_end =3D xdp.= data + frame->len; >>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 xdp.data_meta =3D xdp= .data - frame->metasize; >>>>>> >>>>>> You have not configured xdp.rxq, thus a BPF-prog accessing this=20 >>>>>> will crash. >>>>>> >>>>>> For an XDP TX hook, I want us to provide/give BPF-prog access to=20 >>>>>> some >>>>>> more information about e.g. the current tx-queue length, or TC-q=20 >>>>>> number. >>>>>> >>>>>> Question to Daniel or Alexei, can we do this and still keep=20 >>>>>> BPF_PROG_TYPE_XDP? >>>>>> Or is it better to introduce a new BPF prog type (enum=20 >>>>>> bpf_prog_type) >>>>>> for XDP TX-hook ? >>>>> >>>>> I think a new program type would make the most sense. If/when we >>>>> introduce an XDP TX hook[0], it should have different semantics=20 >>>>> than the >>>>> regular XDP hook. I view the XDP TX hook as a hook that executes=20 >>>>> as the >>>>> very last thing before packets leave the interface. It should have >>>>> access to different context data as you say, but also I don't=20 >>>>> think it >>>>> makes sense to have XDP_TX and XDP_REDIRECT in an XDP_TX hook. And = we >>>>> may also want to have a "throttle" return code; or maybe that=20 >>>>> could be >>>>> done via a helper? >>>>> >>>>> In any case, I don't think this "emulated RX hook on the other end=20 >>>>> of a >>>>> virtual device" model that this series introduces is the right=20 >>>>> semantics >>>>> for an XDP TX hook. I can see what you're trying to do, and for=20 >>>>> virtual >>>>> point-to-point links I think it may make sense to emulate the RX=20 >>>>> hook of >>>>> the "other end" on TX. However, form a UAPI perspective, I don't=20 >>>>> think >>>>> we should be calling this a TX hook; logically, it's still an RX ho= ok >>>>> on the receive end. >>>>> >>>>> If you guys are up for evolving this design into a "proper" TX=20 >>>>> hook (as >>>>> outlined above an in [0]), that would be awesome, of course. But no= t >>>>> sure what constraints you have on your original problem? Do you >>>>> specifically need the "emulated RX hook for unmodified XDP programs= " >>>>> semantics, or could your problem be solved with a TX hook with=20 >>>>> different >>>>> semantics? >>>> >>>> I agree with above. >>>> It looks more like existing BPF_PROG_TYPE_XDP, but attached to egres= s >>>> of veth/tap interface. I think only attachment point makes a=20 >>>> difference. >>>> May be use expected_attach_type ? >>>> Then there will be no need to create new program type. >>>> BPF_PROG_TYPE_XDP will be able to access different fields depending >>>> on expected_attach_type. Like rx-queue length that Jesper is=20 >>>> suggesting >>>> will be available only in such case and not for all=20 >>>> BPF_PROG_TYPE_XDP progs. >>>> It can be reduced too. Like if there is no xdp.rxq concept for=20 >>>> egress side >>>> of virtual device the access to that field can disallowed by the=20 >>>> verifier. >>>> Could you also call it XDP_EGRESS instead of XDP_TX? >>>> I would like to reserve XDP_TX name to what Toke describes as XDP_TX= . >>>> >>> >>> =C2=A0 From the discussion over this set, it makes sense to have new = type of >>> program. As David suggested it will make a way for changes specific >>> to egress path. >>> On the other hand, XDP offload with virtio-net implementation is base= d >>> on "emulated RX hook". How about having this special behavior with >>> expected_attach_type? >> >> Another thought I had re: this was that for these "special" virtual >> point-to-point devices we could extend the API to have an ATTACH_PEER >> flag. So if you have a pair of veth devices (veth0,veth1) connecting t= o >> each other, you could do either of: >> >> bpf_set_link_xdp_fd(ifindex(veth0), prog_fd, 0); >> bpf_set_link_xdp_fd(ifindex(veth1), prog_fd, ATTACH_PEER); >> >> to attach to veth0, and: >> >> bpf_set_link_xdp_fd(ifindex(veth1), prog_fd, 0); >> bpf_set_link_xdp_fd(ifindex(veth0), prog_fd, ATTACH_PEER); >> >> to attach to veth0. >> >> This would allow to attach to a device without having the "other end" >> visible, and keep the "XDP runs on RX" semantics clear to userspace. >> Internally in the kernel we could then turn the "attach to peer" >> operation for a tun device into the "emulate on TX" thing you're alrea= dy >> doing? >> >> Would this work for your use case, do you think? >> >> -Toke >> > > This is nice from UAPI point of view. It may work for veth case but > not for XDP offload with virtio-net. Please see the sequence when > a user program in the guest wants to offload a program to tun. > > * User program wants to loads the program by setting offload flag and > =C2=A0 ifindex: > > - map_offload_ops->alloc() > =C2=A0 virtio-net sends map info to qemu and it creates map on the host= . > - prog_offload_ops->setup() > =C2=A0 New callback just to have a copy of unmodified program. It conta= ins > =C2=A0 original map fds. We replace map fds with fds from the host side= . > =C2=A0 Check the program for unsupported helpers calls. > - prog_offload_ops->finalize() > =C2=A0 Send the program to qemu and it loads the program to the host. > > * User program calls bpf_set_link_xdp_fd() > =C2=A0 virtio-net handles XDP_PROG_SETUP_HW by sending a request to qem= u. > =C2=A0 Qemu then attaches host side program fd to respective tun device= by > =C2=A0 calling bpf_set_link_xdp_fd() > > In above sequence there is no chance to use. For VM, I think what Toke meant is to consider virtio-net as a peer of=20 TAP and we can do something like the following in qemu: bpf_set_link_xdp_fd(ifindex(tap0), prog_fd, ATTACH_PEER); in this case. And the behavior of XDP_TX could be kept as if the XDP was=20 attached to the peer of TAP (actually a virtio-net inside the guest). Thanks > > Here is how other ideas from this discussion can be used: > > - Introduce BPF_PROG_TYPE_TX_XDP for egress path. Have a special > =C2=A0 behavior of emulating RX XDP using expected_attach_type flag. > - The emulated RX XDP will be restrictive in terms of helper calls. > - In offload case qemu will load the program BPF_PROG_TYPE_TX_XDP and > =C2=A0 set expected_attach_type. > > What is your opinion about it? Does the driver implementing egress > XDP needs to know what kind of XDP program it is running? > > Thanks, > Prashant >