From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jacek Milewicz" <jacekowski@jacekowski.org>
Subject: Re: [PATCH] xen-netfront: drop skb when skb->len > 65535
Date: Wed, 6 Mar 2013 18:57:59 +0100 (CET)
Message-ID: <023e01ce1a94$21358280$63a08780$@jacekowski.org>
References: <1362155488-24316-1-git-send-email-wei.liu2@citrix.com>	<5130E9D602000078000C27CC@nat28.tlf.novell.com>	<1362157246.2109.165.camel@zion.uk.xensource.com>	<1362192857.4198.9.camel@hastur.hellion.org.uk>	<20130302133243.GA6846@zion.uk.xensource.com>	<51377AD9.80304@linode.com>
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To: 'Wei Liu' <wei.liu2@citrix.com>, 'Nick Pegg' <npegg@linode.com>
Cc: ij@2013.bluespice.org, 'Ian Campbell' <Ian.Campbell@citrix.com>, konrad.wilk@oracle.com, xen-devel@lists.xen.org, annie.li@oracle.com, 'Jan Beulich' <JBeulich@suse.com>
List-Id: xen-devel@lists.xenproject.org

> On Wed, 2013-03-06 at 17:20 +0000, Nick Pegg wrote:
> > On 3/2/13 8:32 AM, Wei Liu wrote:
> > >
> > > As Nick (npegg@linode.com) pointed out in his email, he saw size
65538.
> > > I can reproduce this as well by setting vif's mtu to 100 then run
iperf.
> > > 100 was just a random number I came up with when I played with
> > > fragmentation.
> > >
> >
> > Wei: How exactly did you set the MTU on the vif and what were your
> > arguments to iperf? I tried this on a test host and was unable to
> > trigger the XSA-39 protection.
> >
> 
> Sorry I didn't state this clearly. I tend to call the interface inside
VM as vif as
> well. I did this inside a VM, ifconfig eth0 mtu 100.
> Nothing fancy added to iperf command line, just `iperf -c XXX` in VM and
> `iperf -s` in host (I limited the test time with -t though).

We have recently hit the same problem (however in our case, larger NFS
transfer was enough to trigger it) and I've found that it only happens if
when MAX_SKB_FRAGS is different on domU and dom0 (as in, domU using older
kernel (without this change
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commi
t/drivers/net/xen-netback/netback.c?id=48856286b64e4b66ec62b94e504d0b29c1a
de664 )) can you confirm your domU kernel version?