net/mlx4_core: Don't fail reg/unreg vlan for older guests

net/mlx4_core: Don't fail reg/unreg vlan for older guests

In upstream kernels under SRIOV, the vlan register/unregister calls
were NOPs (doing nothing and returning OK). We detect these old
calls from guests (via the comm channel), since previously the
port number in mlx4_register_vlan was passed (improperly) in the
out_param. This has been corrected so that the port number is now
passed in bits 8..15 of the in_modifier field.

For old calls, these bits will be zero, so if the passed port
number is zero, we can still look at the out_param field to see
if it contains a valid port number. If yes, the VM is running
an old driver.

Since for old drivers, the register/unregister_vlan wrappers were
NOPs, we continue this policy -- the reason being that upstream
had an additional bug in eth driver running on guests (where
procedure mlx4_en_vlan_rx_kill_vid() had the following code:

if (!mlx4_find_cached_vlan(mdev->dev, priv->port, vid, &idx))
        mlx4_unregister_vlan(mdev->dev, priv->port, idx);
else
        en_err(priv, "could not find vid %d in cache\n", vid);

On a VM, mlx4_find_cached_vlan() will always fail, since the
vlan cache is located on the Hypervisor; on guests it is empty.

Therefore, if we allow upstream guests to register vlans, we will
have vlan leakage since the unregister will never be performed.
Leaving vlan reg/unreg for old guest drivers as a NOP is not a
feature regression, since in upstream the register/unregister
vlan wrapper is a NOP.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>