[ovs-build] Errored: openvswitch/ovs#5921 (branch-2.6 - 2172c6b)

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Wed Feb 14 10:15:00 UTC 2018

Build Update for openvswitch/ovs

Build: #5921
Status: Errored

Duration: 33 minutes and 9 seconds
Commit: 2172c6b (branch-2.6)
Author: Ian Stokes
Message: netdev-dpdk: Fix requested MTU size validation.

This commit replaces MTU_TO_FRAME_LEN(mtu) with MTU_TO_MAX_FRAME_LEN(mtu)
in netdev_dpdk_set_mtu(), in order to determine if the total length of
the L2 frame with an MTU of ’mtu’ exceeds NETDEV_DPDK_MAX_PKT_LEN.

When setting an MTU we first check if the requested total frame length
(which includes associated L2 overhead) will exceed the maximum
frame length supported in netdev_dpdk_set_mtu(). The frame length is
for the device will be set at a later stage in dpdk_eth_dev_init() using

However when using rte_eth_dev_set_mtu(mtu) the calculation used to check
that the frame does not exceed the max frame length for that device varies
between DPDK device drivers. For example ixgbe driver calculates the
frame length for a given MTU as


i40e driver calculates it as


em driver calculates it as


Currently it is possible to set an MTU for a netdev_dpdk device that exceeds
the upper limit MTU for that devices DPDK driver. This leads to a segfault.
This is because the frame length comparison as is, does not take into account
the addition of the vlan tag overhead expected in the drivers. The
netdev_dpdk_set_mtu() call will incorrectly succeed but the subsequent
dpdk_eth_dev_init() will fail before the queues have been created for the
DPDK device. This coupled with assumptions regarding reconfiguration
requirements for the netdev will lead to a segfault when the rxq is
polled for this device.

A simple way to avoid this is by using MTU_TO_MAX_FRAME_LEN(mtu) when
validating a requested MTU in netdev_dpdk_set_mtu().
MTU_TO_MAX_FRAME_LEN(mtu) is equivalent to the following:


By using MTU_TO_MAX_FRAME_LEN at the netdev_dpdk_set_mtu() stage, OvS
now takes into account the maximum L2 overhead that a DPDK driver could
allow for in its frame size calculation. This allows OVS to flag an error
rather than the DPDK driver if the frame length exceeds the max DPDK frame
length. OVS can fail gracefully at this point and use the default MTU of
1500 to continue to configure the port.

Note: this fix is a work around, a better approach would be if DPDK devices
could report the maximum MTU value that can be requested on a per device
basis. This capability however is not currently available. A downside of
this patch is that the MTU upper limit will be reduced by 8 bytes for
DPDK devices that do not need to account for vlan tags in the frame length
driver calculations e.g. ixgbe devices upper MTU limit is reduced from
the OVS point of view from 9710 to 9702.

CC: Mark Kavanagh <mark.b.kavanagh at intel.com>
Fixes: 0072e931 ("netdev-dpdk: add support for jumbo frames")
Signed-off-by: Ian Stokes <ian.stokes at intel.com>
Co-authored-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
Signed-off-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
Acked-by: Flavio Leitner <fbl at sysclose.org>

View the changeset: https://github.com/openvswitch/ovs/compare/d893a3a47501...2172c6b030bf

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