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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 C3AF4C28CBC for ; Wed, 6 May 2020 08:34:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A08B020714 for ; Wed, 6 May 2020 08:34:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YNpcCB/l" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728626AbgEFIez (ORCPT ); Wed, 6 May 2020 04:34:55 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:29028 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726935AbgEFIez (ORCPT ); Wed, 6 May 2020 04:34:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588754093; 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=NFF8NeJjiTbv8THqbxX8heqr35COUx8hMKarYhRqfLk=; b=YNpcCB/lKavYcpYhtnHi17wHmr9UQxNDAwTrf9ipgR0/Apkfnube8QVwKeChHPTWQH4prC k3fBTp+FqewdEDuCPtsnARuLAwlmH5OJDXarJvbMTm25r72Z7hTRJyGwfEiIpFWgoQeRmd OeQvNoKSpYGGqPDd9cI36wFFaiKMwMk= 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-168-QZzC-7xwPoeKQmxnCxlf7w-1; Wed, 06 May 2020 04:34:49 -0400 X-MC-Unique: QZzC-7xwPoeKQmxnCxlf7w-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2DEF11005510; Wed, 6 May 2020 08:34:48 +0000 (UTC) Received: from [10.72.13.165] (ovpn-13-165.pek2.redhat.com [10.72.13.165]) by smtp.corp.redhat.com (Postfix) with ESMTP id 963A460BEC; Wed, 6 May 2020 08:34:38 +0000 (UTC) Subject: Re: [PATCH net-next 1/2] virtio-net: don't reserve space for vnet header for XDP To: Jesper Dangaard Brouer Cc: mst@redhat.com, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, "Jubran, Samih" References: <20200506061633.16327-1-jasowang@redhat.com> <20200506102123.739f1233@carbon> From: Jason Wang Message-ID: <3ecb558b-5281-2497-db3c-6aae7d7f882b@redhat.com> Date: Wed, 6 May 2020 16:34:36 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200506102123.739f1233@carbon> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Content-Transfer-Encoding: quoted-printable Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 2020/5/6 =E4=B8=8B=E5=8D=884:21, Jesper Dangaard Brouer wrote: > On Wed, 6 May 2020 14:16:32 +0800 > Jason Wang wrote: > >> We tried to reserve space for vnet header before >> xdp.data_hard_start. But this is useless since the packet could be >> modified by XDP which may invalidate the information stored in the >> header and > IMHO above statements are wrong. XDP cannot access memory before > xdp.data_hard_start. Thus, it is safe to store a vnet headers before > xdp.data_hard_start. (The sfc driver also use this "before" area). The problem is if we place vnet header before data_hard_start,=20 virtio-net will fail any header adjustment. Or do you mean to copy vnet header before data_hard_start before=20 processing XDP? > >> there's no way for XDP to know the existence of the vnet header curren= tly. > It is true that XDP is unaware of this area, which is the way it > should be. Currently the area will survive after calling BPF/XDP. > After your change it will be overwritten in xdp_frame cases. > > >> So let's just not reserve space for vnet header in this case. > I think this is a wrong approach! > > We are working on supporting GRO multi-buffer for XDP. The vnet header > contains GRO information (see pahole below sign). Another note is that since we need reserve room for skb_shared_info, GRO=20 for XDP may probably lead more frag list. > It is currently not > used in the XDP case, but we will be working towards using it. Good to know that, but I think it can only work when the packet is not=20 modified by XDP? > There > are a lot of unanswered questions on how this will be implemented. > Thus, I cannot layout how we are going to leverage this info yet, but > your patch are killing this info, which IHMO is going in the wrong > direction. I can copy vnet header ahead of data_hard_start, does it work for you? Thanks > > >> Cc: Jesper Dangaard Brouer >> Signed-off-by: Jason Wang >> --- >> drivers/net/virtio_net.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index 11f722460513..98dd75b665a5 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -684,8 +684,8 @@ static struct sk_buff *receive_small(struct net_de= vice *dev, >> page =3D xdp_page; >> } >> =20 >> - xdp.data_hard_start =3D buf + VIRTNET_RX_PAD + vi->hdr_len; >> - xdp.data =3D xdp.data_hard_start + xdp_headroom; >> + xdp.data_hard_start =3D buf + VIRTNET_RX_PAD; >> + xdp.data =3D xdp.data_hard_start + xdp_headroom + vi->hdr_len; >> xdp.data_end =3D xdp.data + len; >> xdp.data_meta =3D xdp.data; >> xdp.rxq =3D &rq->xdp_rxq; >> @@ -845,7 +845,7 @@ static struct sk_buff *receive_mergeable(struct ne= t_device *dev, >> * the descriptor on if we get an XDP_TX return code. >> */ >> data =3D page_address(xdp_page) + offset; >> - xdp.data_hard_start =3D data - VIRTIO_XDP_HEADROOM + vi->hdr_len; >> + xdp.data_hard_start =3D data - VIRTIO_XDP_HEADROOM; >> xdp.data =3D data + vi->hdr_len; >> xdp.data_end =3D xdp.data + (len - vi->hdr_len); >> xdp.data_meta =3D xdp.data; > >