netdev - Re: [PATCH net-next 2/2] mlx4/en_netdev: call notifiers when hw_enc

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Message-ID: <7ec40c37b843ebd3fd2ff5998bb382e13e45d816.camel@redhat.com>
Date:   Fri, 26 Jul 2019 12:39:04 +0200
From:   Davide Caratti <dcaratti@...hat.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Tariq Toukan <tariqt@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     Eran Ben Elisha <eranbe@...lanox.com>
Subject: Re: [PATCH net-next 2/2] mlx4/en_netdev: call notifiers when
 hw_enc_features change

On Thu, 2019-07-25 at 21:27 +0000, Saeed Mahameed wrote:
> On Thu, 2019-07-25 at 14:25 +0200, Davide Caratti wrote:
> > On Wed, 2019-07-24 at 20:47 +0000, Saeed Mahameed wrote:
> > > On Wed, 2019-07-24 at 16:02 +0200, Davide Caratti wrote:
> > > > ensure to call netdev_features_change() when the driver flips its
> > > > hw_enc_features bits.
> > > > 
> > > > Signed-off-by: Davide Caratti <dcaratti@...hat.com>
> > > 
> > > The patch is correct, 
> > 
> > hello Saeed, and thanks for looking at this!
> > 
> > > but can you explain how did you come to this ? 
> > > did you encounter any issue with the current code ?
> > > 
> > > I am asking just because i think the whole dynamic changing of dev-
> > > > hw_enc_features is redundant since mlx4 has the featutres_check
> > > callback.
> > 
> > we need it to ensure that vlan_transfer_features() updates
> > the (new) value of hw_enc_features in the overlying vlan: otherwise,
> > segmentation will happen anyway when skb passes from vxlan to vlan,
> > if the
> > vxlan is added after the vlan device has been created (see:
> > 7dad9937e064
> > ("net: vlan: add support for tunnel offload") ).
> > 
> 
> but in previous patch you made sure that the vlan always sees the
> correct hw_enc_features on driver load, we don't need to have this
> dynamic update mechanism,

ok, but the mlx4 driver flips the value of hw_enc_features when VXLAN
tunnels are added or removed. So, assume eth0 is a Cx3-pro, and I do:
 
 # ip link add name vlan5 link eth0 type vlan id 5
 # ip link add dev vxlan6 type vxlan id 6  [...]  dev vlan5
 
the value of dev->hw_enc_features is 0 for vlan5, and as a consequence
VXLAN over VLAN traffic becomes segmented by the VLAN, even if eth0, at
the end of this sequence, has the "right" features bits.

> features_check ndo should take care of
> protocols we don't support.

I just had a look at mlx4_en_features_check(), I see it checks if the
packet is tunneled in VXLAN and the destination port matches the
configured value of priv->vxlan_port (when that value is not zero). Now:

On Wed, 2019-07-24 at 20:47 +0000, Saeed Mahameed wrote:
> I am asking just because i think the whole dynamic changing of 
> dev-> hw_enc_features is redundant since mlx4 has the featutres_check
> callback.

I read your initial proposal again. Would it be correct if I just use
patch 1/2, where I add an assignment of

dev->hw_enc_features = NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM | \
                       NETIF_F_RXCSUM | \
                       NETIF_F_TSO | NETIF_F_TSO6 | \
                       NETIF_F_GSO_UDP_TUNNEL | \
                       NETIF_F_GSO_UDP_TUNNEL_CSUM | \
                       NETIF_F_GSO_PARTIAL;

in mlx4_en_init_netdev(), and then remove the code that flips
dev->hw_enc_features in mlx4_en_add_vxlan_offloads() and
mlx4_en_del_vxlan_offloads() ?

thanks,
--
davide