From: "Michael S. Tsirkin" <mst@redhat•com>
To: Vlad Yasevich <vyasevic@redhat•com>
Cc: netdev@vger•kernel.org, daniel.lezcano@free•fr,
nightnord@gmail•com, kaber@trash•net, eric.dumazet@gmail•com,
jasowang@redhat•com
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 [thread overview]
Message-ID: <20140423201050.GC28446@redhat.com> (raw)
In-Reply-To: <53581700.9010205@redhat.com>
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 <daniel.lezcano@free•fr>
> >> CC: Patrick McHardy <kaber@trash•net>
> >> CC: Andrian Nord <nightnord@gmail•com>
> >> CC: Eric Dumazet <eric.dumazet@gmail•com>
> >> CC: Michael S. Tsirkin <mst@redhat•com>
> >> CC: Jason Wang <jasowang@redhat•com>
> >> Signed-off-by: Vlad Yasevich <vyasevic@redhat•com>
> >> ---
> >> 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
next prev parent reply other threads:[~2014-04-23 20:10 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-23 16:51 [PATCH 0/2] Fix macvtap checksum errors in bridge mode Vlad Yasevich
2014-04-23 16:51 ` [PATCH 1/2] mactap: Fix checksum errors for non-gso packets " Vlad Yasevich
2014-04-23 19:20 ` Michael S. Tsirkin
2014-04-23 19:39 ` Vlad Yasevich
2014-04-23 20:10 ` Michael S. Tsirkin [this message]
2014-04-23 20:30 ` Vlad Yasevich
2014-04-24 7:26 ` Michael S. Tsirkin
2014-04-24 14:05 ` Vlad Yasevich
2014-04-23 16:51 ` [PATCH 2/2] Revert "macvlan : fix checksums error when we are in bridge mode" Vlad Yasevich
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