Re: [PATCH 0/3] Restore UFO support to virtio_net devices

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 26, 2015 at 05:28:42PM +0200, Michael S. Tsirkin wrote:
> On Mon, Jan 26, 2015 at 09:37:03AM -0500, Vladislav Yasevich wrote:
> > commit 3d0ad09412ffe00c9afa201d01effdb6023d09b4
> > Author: Ben Hutchings <ben@decadent.org.uk>
> > Date:   Thu Oct 30 18:27:12 2014 +0000
> > 
> >     drivers/net: Disable UFO through virtio
> > 
> > Turned off UFO support to virtio-net based devices due to issues
> > with IPv6 fragment id generation for UFO packets.  The issue
> > was that IPv6 UFO/GSO implementation expects the fragment id
> > to be supplied in skb_shinfo().  However, for packets generated
> > by the VMs, the fragment id is not supplied which causes all
> > IPv6 fragments to have the id of 0.
> > 
> > The problem is that turning off UFO support on tap/macvtap
> > as well as virtio devices caused issues with migrations.  
> > Migrations would fail when moving a vm from a kernel supporting
> > expecting UFO to work to the newer kernels that disabled UFO.
> > 
> > This series provides a partial solution to address the migration
> > issue.  The series reserves a bit in the skb and sets the bit
> > with the ipv6 fragment id has been generated for the packet.
> > UFO/GSO code then checks the bit to see if the fragment id
> > is already present or if a new fragment id needs to be generated.
> > This solution allows host-originated UFO packets to keep a
> > better randomized fragment id, as well as generating a randomized
> > id for VM generated traffic (solving the fragment id 0 issue).
> > 
> > Vladislav Yasevich (3):
> >   ipv6: Select fragment id during UFO/GSO segmentation if not set.
> >   Revert "drivers/net, ipv6: Select IPv6 fragment idents for virtio UFO
> >     packets"
> >   Revert "drivers/net: Disable UFO through virtio"
> > 
> >  drivers/net/macvtap.c    | 16 ++++++++--------
> >  drivers/net/tun.c        | 25 +++++++++----------------
> >  drivers/net/virtio_net.c | 24 ++++++++++--------------
> >  include/linux/skbuff.h   |  3 ++-
> >  include/net/ipv6.h       |  2 ++
> >  net/ipv6/ip6_output.c    |  4 ++--
> >  net/ipv6/output_core.c   |  9 ++++++++-
> >  net/ipv6/udp_offload.c   | 10 +++++++++-
> >  8 files changed, 50 insertions(+), 43 deletions(-)
> 
> Should also help a lot to put UDP performance where it was.
> 
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> 

BTW these might also be a good stable candidate.

> 
> > -- 
> > 1.9.3