Re: [PATCH] virtio: Work around frames incorrectly marked as gso

On Wed, Feb 12, 2020 at 10:03:31AM +0000, Anton Ivanov wrote:

On 11/02/2020 10:37, Michael S. Tsirkin wrote:

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On Tue, Feb 11, 2020 at 07:42:37AM +0000, Anton Ivanov wrote:

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On 11/02/2020 02:51, Jason Wang wrote:

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On 2020/2/11 上午12:55, Anton Ivanov wrote:

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On 09/12/2019 10:48, anton.ivanov@cambridgegreys.com wrote:

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From: Anton Ivanov <anton.ivanov@cambridgegreys.com>

Some of the frames marked as GSO which arrive at
virtio_net_hdr_from_skb() have no GSO_TYPE, no
fragments (data_len = 0) and length significantly shorter
than the MTU (752 in my experiments).

This is observed on raw sockets reading off vEth interfaces
in all 4.x and 5.x kernels I tested.

These frames are reported as invalid while they are in fact
gso-less frames.

This patch marks the vnet header as no-GSO for them instead
of reporting it as invalid.

Signed-off-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
---
   include/linux/virtio_net.h | 8 ++++++--
   1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 0d1fe9297ac6..d90d5cff1b9a 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h

@@ -112,8 +112,12 @@ static inline int

virtio_net_hdr_from_skb(const struct sk_buff *skb,
               hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
           else if (sinfo->gso_type & SKB_GSO_TCPV6)
               hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
-        else
-            return -EINVAL;
+        else {
+            if (skb->data_len == 0)
+                hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE;
+            else
+                return -EINVAL;
+        }
           if (sinfo->gso_type & SKB_GSO_TCP_ECN)
               hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN;
       } else

ping.

Do you mean gso_size is set but gso_type is not? Looks like a bug
elsewhere.

Thanks

Yes.

I could not trace it where it is coming from.

I see it when doing recvmmsg on raw sockets in the UML vector network
drivers.

I think we need to find the culprit and fix it there, lots of other things
can break otherwise.
Just printing out skb->dev->name should do the trick, no?

I will rebuild my rig and retest (it's been a while since I worked on this bug).

In theory, it should be veth - the test is over a vEth pair and all frames are locally originated by iperf.

In practice - I will retest and post the results sometimes later today.

Brgds,

ok if it's veth then you need to add a similar printk patch to veth
and re-run to see where does it come from originally.

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quoted

-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/

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-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/