From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 1/2] mactap: Fix checksum errors for non-gso packets in bridge mode Date: Wed, 23 Apr 2014 23:10:50 +0300 Message-ID: <20140423201050.GC28446@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> <53581700.9010205@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, daniel.lezcano@free.fr, nightnord@gmail.com, kaber@trash.net, eric.dumazet@gmail.com, jasowang@redhat.com To: Vlad Yasevich Return-path: Received: from mx1.redhat.com ([209.132.183.28]:1325 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754008AbaDWUKt (ORCPT ); Wed, 23 Apr 2014 16:10:49 -0400 Content-Disposition: inline In-Reply-To: <53581700.9010205@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Apr 23, 2014 at 03:39:44PM -0400, Vlad Yasevich wrote: > 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. Seems cleaner to test a single bit otherwise one is left wondering what happens if only one bit matches. > > > > 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. Hmm how do we know it's not a gso packet? All I see is need_gso test which means it needs segmentation. > Also, other offloads are dependent on checksum. > > -vlad Right so what if checksum is on, but segmentation is off? Not the case with e1000 today but can be with other userspace. > > > >> skb_queue_tail(&q->sk.sk_receive_queue, skb); > >> } > >> > >> -- > >> 1.9.0