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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 26 Jan 2015 17:28:42 +0200

On Mon, Jan 26, 2015 at 09:37:03AM -0500, Vladislav Yasevich wrote:
> commit 3d0ad09412ffe00c9afa201d01effdb6023d09b4
> Author: Ben Hutchings <[email-masked]>
> 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 <[email-masked]>

> -- 
> 1.9.3