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=-7.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 4A560C4743C for ; Mon, 21 Jun 2021 20:44:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 25902611CE for ; Mon, 21 Jun 2021 20:44:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231162AbhFUUqS (ORCPT ); Mon, 21 Jun 2021 16:46:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58944 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229940AbhFUUqR (ORCPT ); Mon, 21 Jun 2021 16:46:17 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B0CC1C061574 for ; Mon, 21 Jun 2021 13:44:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Mime-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=EVbOZfkdB2wvCaBcQ2HNWwdx3PJycn3QNw1BLMAd1vI=; b=3bzpG9jm1kpXg4NQoTgYO28UdJ y5thHRDkl43MRIaIQ+OGMKZSLNmVYOMJQQqZl9Yl2FXomNpNymfiZhKZKOYsRu2TXKrKRqIY0Ek/h 5ZwxgY9EvhBrVrrbLgH1K6Tx80f7xbnuN9ifEDsmibGM+ZuJ5qxWF1zGFwX9GhtWWJ2ccPjNoue2A 5wAvirDplkokfM5oXgIDs33/vxbXywo6q70IGg+0JSGSvIM9D7ZDK8H5smromFa21v092yt7ohBzw JvfCm+QGviwWX0Mu1k9uCgtleclJ2tNHKWorBN+jGMR13mplA3aiBCESmTuA0a8aM18ZFO6akBht6 T7WmzNDg==; Received: from [2001:8b0:10b:1::3ae] (helo=u3832b3a9db3152.ant.amazon.com) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1lvQm1-004pcn-F8; Mon, 21 Jun 2021 20:44:01 +0000 Message-ID: Subject: Re: [PATCH] net: tun: fix tun_xdp_one() for IFF_TUN mode From: David Woodhouse To: Jason Wang , netdev Cc: Eugenio =?ISO-8859-1?Q?P=E9rez?= Date: Mon, 21 Jun 2021 21:43:59 +0100 In-Reply-To: <2433592d2b26deec33336dd3e83acfd273b0cf30.camel@infradead.org> References: <03ee62602dd7b7101f78e0802249a6e2e4c10b7f.camel@infradead.org> <2cbe878845eb2a1e3803b3340263ea14436fe053.camel@infradead.org> <2433592d2b26deec33336dd3e83acfd273b0cf30.camel@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-JeIBEVYO+vuGLVMObiA+" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org --=-JeIBEVYO+vuGLVMObiA+ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2021-06-21 at 15:50 +0100, David Woodhouse wrote: > On Mon, 2021-06-21 at 11:52 +0100, David Woodhouse wrote: > >=20 > > Firstly, I don't think I can set IFF_VNET_HDR on the tun device after > > opening it. So my model of "open the tun device, then *see* if we can > > use vhost to accelerate it" doesn't work. > >=20 > > I tried setting VHOST_NET_F_VIRTIO_NET_HDR in the vhost features > > instead, but that gives me a weird failure mode where it drops around > > half the incoming packets, and I haven't yet worked out why. >=20 > FWIW that problem also goes away if I set TUNSNDBUF and avoid the XDP > data path. Looks like there are two problems there. Firstly, vhost_net_build_xdp() doesn't cope well with sock_hlen being zero. It reads those zero bytes into its buffer, then points 'gso' at the buffer with no valid data in it, and checks gso->flags for the NEEDS_CSUM flag. Secondly, tun_xdp_one() doesn't cope with receiving packets without the virtio header either. While tun_get_user() correctly checks IFF_VNET_HDR, tun_xdp_one() does not, and treats the start of my IP packets as if they were a virtio_net_hdr. I'll look at turning my code into a test case for kernel selftests. --=-JeIBEVYO+vuGLVMObiA+ Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCECow ggUcMIIEBKADAgECAhEA4rtJSHkq7AnpxKUY8ZlYZjANBgkqhkiG9w0BAQsFADCBlzELMAkGA1UE BhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEaMBgG A1UEChMRQ09NT0RPIENBIExpbWl0ZWQxPTA7BgNVBAMTNENPTU9ETyBSU0EgQ2xpZW50IEF1dGhl bnRpY2F0aW9uIGFuZCBTZWN1cmUgRW1haWwgQ0EwHhcNMTkwMTAyMDAwMDAwWhcNMjIwMTAxMjM1 OTU5WjAkMSIwIAYJKoZIhvcNAQkBFhNkd213MkBpbmZyYWRlYWQub3JnMIIBIjANBgkqhkiG9w0B AQEFAAOCAQ8AMIIBCgKCAQEAsv3wObLTCbUA7GJqKj9vHGf+Fa+tpkO+ZRVve9EpNsMsfXhvFpb8 RgL8vD+L133wK6csYoDU7zKiAo92FMUWaY1Hy6HqvVr9oevfTV3xhB5rQO1RHJoAfkvhy+wpjo7Q cXuzkOpibq2YurVStHAiGqAOMGMXhcVGqPuGhcVcVzVUjsvEzAV9Po9K2rpZ52FE4rDkpDK1pBK+ 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