netdev - Re: [PATCH net] xen-netback: fix gso

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Date:	Thu, 12 Dec 2013 14:42:22 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Paul Durrant <paul.durrant@...rix.com>
CC:	<xen-devel@...ts.xen.org>, <netdev@...r.kernel.org>,
	Wei Liu <wei.liu2@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>
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@...rix.com>
> Cc: Wei Liu <wei.liu2@...rix.com>
> Cc: Ian Campbell <ian.campbell@...rix.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> ---
>  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@...rix.com>

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.

Ian.

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