From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Egger Subject: Re: [Xen-devel] [PATCH 2/4] xen-netfront: drop skb when skb->len > 65535 Date: Tue, 9 Apr 2013 16:53:13 +0200 Message-ID: <51642B59.4080407@amazon.de> References: <1363602955-24790-1-git-send-email-wei.liu2@citrix.com> <1363602955-24790-3-git-send-email-wei.liu2@citrix.com> <1363606970.30193.22.camel@zakaz.uk.xensource.com> <1363617642.29093.203.camel@zion.uk.xensource.com> <1363618459.2963.10.camel@zakaz.uk.xensource.com> <1363619098.29093.205.camel@zion.uk.xensource.com> <1363619244.2963.11.camel@zakaz.uk.xensource.com> <1363728289.31336.7.camel@deadeye.wl.decadent.org.uk> <1363728480.31336.10.camel@deadeye.wl.decadent.org.uk> <1365517818.10725.44.camel@zakaz.uk.xensource.com> <1365518703.2623.6.camel@bwh-desktop.uk.solarflarecom.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: Ian Campbell , "netdev@vger.kernel.org" , "annie.li@oracle.com" , "konrad.wilk@oracle.com" , Wei Liu , "xen-devel@lists.xen.org" To: Ben Hutchings Return-path: Received: from smtp-fw-2101.amazon.com ([72.21.196.25]:5519 "EHLO smtp-fw-2101.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1765005Ab3DIOxa (ORCPT ); Tue, 9 Apr 2013 10:53:30 -0400 In-Reply-To: <1365518703.2623.6.camel@bwh-desktop.uk.solarflarecom.com> Sender: netdev-owner@vger.kernel.org List-ID: On 09.04.13 16:45, Ben Hutchings wrote: > On Tue, 2013-04-09 at 15:30 +0100, Ian Campbell wrote: >> On Tue, 2013-03-19 at 21:28 +0000, Ben Hutchings wrote: >>> On Tue, 2013-03-19 at 21:24 +0000, Ben Hutchings wrote: >>>> On Mon, 2013-03-18 at 15:07 +0000, Ian Campbell wrote: >>>>> On Mon, 2013-03-18 at 15:04 +0000, Wei Liu wrote: >>>>>> On Mon, 2013-03-18 at 14:54 +0000, Ian Campbell wrote: >>>>>>> On Mon, 2013-03-18 at 14:40 +0000, Wei Liu wrote: >>>>>>>> On Mon, 2013-03-18 at 11:42 +0000, Ian Campbell wrote: >>>>>>>>> On Mon, 2013-03-18 at 10:35 +0000, Wei Liu wrote: >>>>>>>>>> The `size' field of Xen network wire format is uint16_t, anything bigger than >>>>>>>>>> 65535 will cause overflow. >>>>>>>>>> >>>>>>>>>> Signed-off-by: Wei Liu >>>>>>>>>> --- >>>>>>>>>> drivers/net/xen-netfront.c | 12 ++++++++++++ >>>>>>>>>> 1 file changed, 12 insertions(+) >>>>>>>>>> >>>>>>>>>> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c >>>>>>>>>> index 5527663..8c3d065 100644 >>>>>>>>>> --- a/drivers/net/xen-netfront.c >>>>>>>>>> +++ b/drivers/net/xen-netfront.c >>>>>>>>>> @@ -547,6 +547,18 @@ static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev) >>>>>>>>>> unsigned int len = skb_headlen(skb); >>>>>>>>>> unsigned long flags; >>>>>>>>>> >>>>>>>>>> + /* >>>>>>>>>> + * wire format of xen_netif_tx_request only supports skb->len >>>>>>>>>> + * < 64K, because size field in xen_netif_tx_request is >>>>>>>>>> + * uint16_t. >>>>>>>>> >>>>>>>>> Is there some field we can set e.g. in struct ethernet_device which >>>>>>>>> would stop this from happening? >>>>>>>>> >>>>>>>> >>>>>>>> struct ethernet_device? I could not find it. >>>>>>>> >>>>>>>> And for struct net_device, >>>>>>> >>>>>>> I meant struct net_device. >>>>>>> >>>>>>>> there is no field for this AFAICT. >>>>>>> >>>>>>> Interesting. Are hardware devices expected to cope with arbitrary sized >>>>>>> GSO skbs then I wonder. >>>>>>> >>>>>> >>>>>> No idea. But there is a macro called GSO_MAX_SIZE (65536) in struct >>>>>> net_device. :-) >>>>> >>>>> But aren't we seeing skb's bigger than that? >>>>> >>>>> Maybe this is just a historical bug in some older guests? >>>> >>>> GSO_MAX_SIZE is the maximum payload length, not the maximum total length >>>> of an skb. >>> >>> ...and it's actually just the default value assigned to >>> dev->gso_max_size. You'll want to change it to your actual maximum >>> (65535 - maximum length of headers) before registering your net devices. >> >> Thanks. >> >> "maximum length of headers" might be a bit tricky to determine >> generically :-(. > > Well you don't need to be generic, you need to know the maximum length > of headers that might appear in a TSO skb. > > Ethernet + VLAN tag + IPv6 + TCP + timestamp option = 90 bytes, but I'm > not sure whether there can be other IP or TCP options in a TSO skb. I'd > really like to get the TSO requirements clearly documented somewhere. What about encapsulated IPSEC, IP-in-IP-tunnels, etc. ? Christoph