Re: [Xen-devel] [PATCH net] xen-netback: fix gso_prefix check

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Ian Campbell
> Sent: 12 December 2013 14:42
> To: Paul Durrant
> Cc: xen-devel@xxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; Wei Liu; David Vrabel
> Subject: Re: [PATCH net] xen-netback: fix gso_prefix check
> 
> On Thu, 2013-12-12 at 14:20 +0000, Paul Durrant wrote:
> > There is a mistake in checking the gso_prefix mask when passing large
> > packets to a guest. The wrong shift is applied to the bit - the raw skb
> > gso type is used rather then the translated one. This leads to large packets
> > being handed to the guest without the GSO metadata. This patch fixes the
> > check.
> >
> > The mistake manifested as errors whilst running Microsoft HCK large packet
> > offload tests between a pair of Windows 8 VMs. I have verified this patch
> > fixes those errors.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> > Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> > Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> > ---
> >  drivers/net/xen-netback/netback.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-
> netback/netback.c
> > index 56c3e5a..999e290 100644
> > --- a/drivers/net/xen-netback/netback.c
> > +++ b/drivers/net/xen-netback/netback.c
> > @@ -452,7 +452,7 @@ static int xenvif_gop_skb(struct sk_buff *skb,
> >     }
> >
> >     /* Set up a GSO prefix descriptor, if necessary */
> > -   if ((1 << skb_shinfo(skb)->gso_type) & vif->gso_prefix_mask) {
> > +   if ((1 << gso_type) & vif->gso_prefix_mask) {
> 
> gso_type here is XEN_NETIF_GSO_TYPE_TCPV4, vif->gso_prefix_mask is
> initialised with GSO_BIT(TCPV4) et al. Where
>         #define GSO_BIT(type) \
>                 (1 << XEN_NETIF_GSO_TYPE_ ## type)
> 
> So,
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> 
> But it might be nice to use BIT() from bitops.h for both GSO_BIT and the
> check, since it took me quite a bit of wandering around to figure out
> how these ended up the same.
> 

Ok. I'll come up with a separate patch for that.

  Paul
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