[net] ixgbe: fix parsing of TC actions for HW offload

[net] ixgbe: fix parsing of TC actions for HW offload

[Jeff Kirsher]

From: Ondřej Hlavatý <ohlavaty@redhat.com>

The previous code was optimistic, accepting the offload of whole action
chain when there was a single known action (drop/redirect). This results
in offloading a rule which should not be offloaded, because its behavior
cannot be reproduced in the hardware.

For example:

$ tc filter add dev eno1 parent ffff: protocol ip \
    u32 ht 800: order 1 match tcp src 42 FFFF \
    action mirred egress mirror dev enp1s16 pipe \
    drop

The controller is unable to mirror the packet to a VF, but still
offloads the rule by dropping the packet.

Change the approach of the function to a pessimistic one, rejecting the
chain when an unknown action is found. This is better suited for future
extensions.

Note that both recognized actions always return TC_ACT_SHOT, therefore
it is safe to ignore actions behind them.

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Ondřej Hlavatý <ohlavaty@redhat.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index afadba99f7b8..d01e1f0280cf 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -9054,7 +9054,6 @@ static int parse_tc_actions(struct ixgbe_adapter *adapter,
 {
 	const struct tc_action *a;
 	LIST_HEAD(actions);
-	int err;
 
 	if (!tcf_exts_has_actions(exts))
 		return -EINVAL;
@@ -9075,14 +9074,14 @@ static int parse_tc_actions(struct ixgbe_adapter *adapter,
 
 			if (!dev)
 				return -EINVAL;
-			err = handle_redirect_action(adapter, dev->ifindex, queue,
-						     action);
-			if (err == 0)
-				return err;
+			return handle_redirect_action(adapter, dev->ifindex,
+						      queue, action);
 		}
+
+		return -EINVAL;
 	}
 
-	return -EINVAL;
+	return 0;
 }
 #else
 static int parse_tc_actions(struct ixgbe_adapter *adapter,
-- 
2.17.0

Re: [net] ixgbe: fix parsing of TC actions for HW offload

[David Miller]

From: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Date: Wed, 30 May 2018 11:01:34 -0700

> From: Ondřej Hlavatý <ohlavaty@redhat.com>
> 
> The previous code was optimistic, accepting the offload of whole action
> chain when there was a single known action (drop/redirect). This results
> in offloading a rule which should not be offloaded, because its behavior
> cannot be reproduced in the hardware.
> 
> For example:
> 
> $ tc filter add dev eno1 parent ffff: protocol ip \
>     u32 ht 800: order 1 match tcp src 42 FFFF \
>     action mirred egress mirror dev enp1s16 pipe \
>     drop
> 
> The controller is unable to mirror the packet to a VF, but still
> offloads the rule by dropping the packet.
> 
> Change the approach of the function to a pessimistic one, rejecting the
> chain when an unknown action is found. This is better suited for future
> extensions.
> 
> Note that both recognized actions always return TC_ACT_SHOT, therefore
> it is safe to ignore actions behind them.
> 
> Cc: Jamal Hadi Salim <jhs@mojatatu.com>
> Cc: Jiri Pirko <jiri@resnulli.us>
> Signed-off-by: Ondřej Hlavatý <ohlavaty@redhat.com>
> Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

This introduces a new warning with gcc-8.1.1 on Fedora 28.

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c: In function ‘ixgbe_configure_clsu32’:
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c:9311:8: warning: ‘queue’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  err = ixgbe_fdir_write_perfect_filter_82599(hw, &input->filter,
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           input->sw_idx, queue);
           ~~~~~~~~~~~~~~~~~~~~~

Re: [net] ixgbe: fix parsing of TC actions for HW offload

[Ondřej Hlavatý]

On 31.05., David Miller wrote:
> From: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
> Date: Wed, 30 May 2018 11:01:34 -0700
> 
> > From: Ondřej Hlavatý <ohlavaty@redhat.com>
> > 
> > The previous code was optimistic, accepting the offload of whole action
> > chain when there was a single known action (drop/redirect). This results
> > in offloading a rule which should not be offloaded, because its behavior
> > cannot be reproduced in the hardware.
> > 
> 
> This introduces a new warning with gcc-8.1.1 on Fedora 28.

Indeed. Sorry for noticing that it was introduced by my patch. The
issue is pretty obvious - empty action chain will not select a queue. As
the Flow Director rules always need to explicitly set a queue index when
they match (as far as I'm concerned), the correct solution should be to
just reject empty chains for offload as well. I will prepare v2 soon.

Ondřej