Re: [Xen-devel] Bug in hash changes to netback in 4.7.2 kernel

[Anthony Wright <anthony@xxxxxxxxxxxxxxx>]

On 06/09/2016 13:57, Paul Durrant wrote:
>> -----Original Message-----
>> From: Anthony Wright [mailto:anthony@xxxxxxxxxxxxxxx]
>> Sent: 06 September 2016 13:23
>> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
>> Cc: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
>> Subject: Bug in hash changes to netback in 4.7.2 kernel
>>
>> When I run Xen (4.7.0) nested in VirtualBox (5.0.24_Ubuntu r108355) with a
>> linux-4.7.2 Dom0 kernel, none of my DomU's (linux-3.17.3) have network
>> connectivity because they reject all packets with the error 'Invalid extra 
>> type:
>> 4'. When I run exactly the same setup on bare metal, I don't get the error
>> messages.
>>
>> From poking around in the code this seems to be because the 4.7.2 kernel
>> wrongly decides that the DomU's will understand EXTRA_TYPE_HASH, and so
>> attach it to the network packet. Since the DomU's don't understand the extra
>> info their netfront driver rejects the whole packet.
> The code in xenvif_select_queue() deliberately clears the skb->sw_hash field 
> (which gates adding the new extra type) if the hash algorithm selected by the 
> frontend is 'none', which should be the default. So, unless you have a 
> frontend that is implementing the control ring protocol, but failing to 
> recognize the new extra type I'm not how you're seeing the problem... unless 
> somehow a packet which hash is getting into netback's start_xmit without 
> first having gone through select_queue?
I very much doubt that the frontend is implementing the control ring
protocol, the DomUs are running stock linux-3.17.3. I build the system
from source, so happy to re-compile with debug code.

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