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[Xen-devel] Checksumming problem in pv_ops dom0 kernel / netback

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Subject: [Xen-devel] Checksumming problem in pv_ops dom0 kernel / netback
From: "S.H. Verbrugge" <ief@xxxxxxxxx>
Date: Wed, 17 Mar 2010 13:34:48 +0100
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I seem to be having some troubles regarding the latest and 
Xen dom0 pv_ops trees.

Our platform:

-Xen 3.4.3-rc3 (also tried 3.4.2 on pv_ops dom0) 
- pv_ops dom0 kernel, perhaps a week old checkout from xen/stable git 
(can provide changeset if requested).
-100+ domU's, all PV.

Ever since we switched to a pv_ops dom0 kernel (we were using 2.6.26 xenkernel 
from Debian repo before, with Xen 3.2),
we started to have some problems when attempting to route packets on a domU.

The following message appears in dmesg on the dom0:

"Attempting to checksum a non-TCP/UDP packet, dropping a protocol 1 packet"

We can actually sniff both the virtual interface on the dom0 (nothing ever 
leaves the domU) and 
we do see the ICMP echo requests inside the domU. The reply, however, never 
gets to the destination or outside the domU for that matter.

It seems that for some reason, as soon as the packet leaves the domU, the dom0 
kernel drops the packet, as shown in the dmesg log.

Some background info:

We're using normal virtual interfaces, on a named bridge, br-internet. This 
bridge contains the hardware interface 'eth0'.
This is a tg3 interface, we already tried turning off both RX and TX 
checksumming for this interface.
Setting 'ethtool tx off' in the domU itself, doesn't help, either.

The different interfaces are vlan'ed through a Cisco 2927 switch.

Since this problem did not occur in xenkernels before, it is most likely 
related to a netback patch in pv_ops dom0.
Perhaps somebody could provide me with some more info, or insights.

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