From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: [PATCH 1/2] mactap: Fix checksum errors for non-gso packets in bridge mode Date: Wed, 23 Apr 2014 15:39:44 -0400 Message-ID: <53581700.9010205@redhat.com> References: <1398271901-32534-1-git-send-email-vyasevic@redhat.com> <1398271901-32534-2-git-send-email-vyasevic@redhat.com> <20140423192022.GA28446@redhat.com> Reply-To: vyasevic@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, daniel.lezcano@free.fr, nightnord@gmail.com, kaber@trash.net, eric.dumazet@gmail.com, jasowang@redhat.com To: "Michael S. Tsirkin" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:50824 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757238AbaDWTjv (ORCPT ); Wed, 23 Apr 2014 15:39:51 -0400 In-Reply-To: <20140423192022.GA28446@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On 04/23/2014 03:20 PM, Michael S. Tsirkin wrote: > On Wed, Apr 23, 2014 at 12:51:40PM -0400, Vlad Yasevich wrote: >> The following is a problematic configuration: >> >> VM1: virtio-net device connected to macvtap0@eth0 >> VM2: e1000 device connect to macvtap1@eth0 >> >> The problem is is that virtio-net supports checksum offloading >> and thus sends the packets to the host with CHECKSUM_PARTIAL set. >> On the other hand, e1000 does not support any acceleration. >> >> For small TCP packets (and this includes the 3-way handshake), >> e1000 ends up receiving packets that only have a partial checksum >> set. This causes TCP to fail checksum validation and to drop >> packets. As a result tcp connections can not be established. >> >> Commit 3e4f8b787370978733ca6cae452720a4f0c296b8 >> macvtap: Perform GSO on forwarding path. >> fixes this issue for large packets wthat will end up undergoing GSO. >> This commit adds a check for the non-GSO case and attempts to >> compute the checksum for partially checksummed packets in the >> non-GSO case. >> >> CC: Daniel Lezcano >> CC: Patrick McHardy >> CC: Andrian Nord >> CC: Eric Dumazet >> CC: Michael S. Tsirkin >> CC: Jason Wang >> Signed-off-by: Vlad Yasevich >> --- >> drivers/net/macvtap.c | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c >> index ff111a8..ba91084 100644 >> --- a/drivers/net/macvtap.c >> +++ b/drivers/net/macvtap.c >> @@ -322,6 +322,13 @@ static rx_handler_result_t macvtap_handle_frame(struct sk_buff **pskb) >> segs = nskb; >> } >> } else { >> + /* If we receive a partial checksum and the tap side >> + * doesn't support checksum offload, compute the checksum. >> + */ >> + if (skb->ip_summed == CHECKSUM_PARTIAL && >> + !(features & NETIF_F_ALL_CSUM) && >> + skb_checksum_help(skb)) >> + goto drop; > > Hmm confused by NETIF_F_ALL_CSUM here. > > features come from here: > feature_mask = NETIF_F_HW_CSUM; > > if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) { > if (arg & TUN_F_TSO_ECN) > feature_mask |= NETIF_F_TSO_ECN; > if (arg & TUN_F_TSO4) > feature_mask |= NETIF_F_TSO; > if (arg & TUN_F_TSO6) > feature_mask |= NETIF_F_TSO6; > } > > if (arg & TUN_F_UFO) > feature_mask |= NETIF_F_UFO; > > > okay so why not just check that NETIF_F_HW_CSUM is set? We can do that, but it doesn't make much difference. > > Also does it matter whether specific offloads are enabled? > No it doesn't matter at all. The packet is not a GSO packet so no other acceleration is used. Also, other offloads are dependent on checksum. -vlad > >> skb_queue_tail(&q->sk.sk_receive_queue, skb); >> } >> >> -- >> 1.9.0