IPv6 UFO for VMs

[Ben Hutchings <ben@decadent.org.uk>]

[-- Attachment #1.1: Type: text/plain, Size: 1303 bytes --]

There are several ways that VMs can take advantage of UFO and get the
host to do fragmentation for them:

drivers/net/macvtap.c:                  gso_type = SKB_GSO_UDP;
drivers/net/tun.c:                      skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
drivers/net/virtio_net.c:                       skb_shinfo(skb)->gso_type = SKB_GSO_UDP;

Our implementation of UFO for IPv6 does:

		fptr = (struct frag_hdr *)(skb_network_header(skb) + unfrag_ip6hlen);
		fptr->nexthdr = nexthdr;
		fptr->reserved = 0;
		fptr->identification = skb_shinfo(skb)->ip6_frag_id;

which assumes ip6_frag_id has been set.  That's only true if the local
stack constructed the skb; otherwise it appears we get zero.

This seems to be a regression as a result of:

commit 916e4cf46d0204806c062c8c6c4d1f633852c5b6
Author: Hannes Frederic Sowa <hannes@stressinduktion.org>
Date:   Fri Feb 21 02:55:35 2014 +0100

    ipv6: reuse ip6_frag_id from ip6_ufo_append_data

However, that change seems reasonable - we *shouldn't* be choosing IDs
for any other stack.  Any paravirt net driver that can use IPv6 UFO
needs to have some way of passing a fragmentation ID to put in
skb_shared_info::ip6_frag_id.

Ben.

-- 
Ben Hutchings
For every action, there is an equal and opposite criticism. - Harrison

[-- Attachment #1.2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 811 bytes --]

[-- Attachment #2: Type: text/plain, Size: 183 bytes --]

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization