netdev - Re: [PATCH v3 1/2] macvtap: include all checksum offloads in TUN

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Date:	Thu, 15 Aug 2013 21:52:10 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Vlad Yasevich <vyasevic@...hat.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH v3 1/2] macvtap: include all checksum offloads in
 TUN_OFFLOAD mask

On Thu, Aug 15, 2013 at 02:45:30PM -0400, Vlad Yasevich wrote:
> On 08/15/2013 02:24 PM, Michael S. Tsirkin wrote:
> >On Thu, Aug 15, 2013 at 01:02:52PM -0400, Vlad Yasevich wrote:
> >>The features of the macvlan are based on the features of lower
> >>device and thus can have checksum featurs other then IFF_F_HW_CSUM
> >
> >s/featurs/features/
> >
> >:set spell spelllang=en_us
> >
> >or whatever's the equivalent in your editor of choice.
> >
> >>set.  However, TUN_OFFLOAD mask only includes IFF_F_HW_CSUM.  Thus
> >>when performing gso segmentation during macvtap_forward(),
> >>it is possbile to end up with skbs that have ip_summed set
> >>to CHECKSUM_PARTIAL.  This is incorrect when the user
> >>turns off checksum offloading.
> >>
> >>Include all possible checksum offload values so that
> >>we'll properly mask them off when performing GSO.
> >>
> >>Signed-off-by: Vlad Yasevich <vyasevic@...hat.com>
> >>---
> >>  drivers/net/macvtap.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >>diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> >>index b51db2a..8121358 100644
> >>--- a/drivers/net/macvtap.c
> >>+++ b/drivers/net/macvtap.c
> >>@@ -65,7 +65,7 @@ static struct cdev macvtap_cdev;
> >>
> >>  static const struct proto_ops macvtap_socket_ops;
> >>
> >>-#define TUN_OFFLOADS (NETIF_F_HW_CSUM | NETIF_F_TSO_ECN | NETIF_F_TSO | \
> >>+#define TUN_OFFLOADS (NETIF_F_ALL_CSUM | NETIF_F_TSO_ECN | NETIF_F_TSO | \
> >>  		      NETIF_F_TSO6 | NETIF_F_UFO)
> >>  #define RX_OFFLOADS (NETIF_F_GRO | NETIF_F_LRO)
> >>  /*
> >
> >Okay so you are talking about hardware that sets some other
> >checksum bit besides HW_CSUM, e.g. IP_CSUM, so
> >
> >         vlan->tap_features = vlan->dev->features &
> >                             (feature_mask | ~TUN_OFFLOADS);
> >
> >will not clear IP_CSUM even if feature_mask is 0.
> >
> >Maybe mention this in the changelog, in case user
> >will wonder whether his hardware is affected.
> >
> >So I agree, that's a bug, but if you make this change the reverse will hold
> >(on this hardware):
> >if user sets TUN_F_CSUM, we won't set NETIF_F_IP_CSUM
> >so checksum offloading won't work.
> >
> >So I think you want s/NETIF_F_HW_CSUM/NETIF_F_ALL_CSUM/ everywhere
> >and not just in this place.
> 
> Yes.  I thought about that, but forgot to do in this patch set.
> 
> >
> >Also - Cc stable?
> >
> 
> The offloads work went into 3.11, so I don't think there is a need
> for stable.

Right. Thanks for the correction.

> -vlad
> >
> >>--
> >>1.8.1.4
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