Re: [Intel-wired-lan] [PATCH v5] ixgbe: Add module parameter to disable VLAN filter

From: Alexander Duyck
Date: Tue May 26 2015 - 21:43:25 EST

On 05/26/2015 06:11 PM, Hiroshi Shimamoto wrote:
On 05/21/2015 06:10 AM, Hiroshi Shimamoto wrote:
From: Hiroshi Shimamoto <h-shimamoto@xxxxxxxxxxxxx>

Introduce module parameter "disable_hw_vlan_filter" to disable HW VLAN
filter on ixgbe module load.

From the hardware limitation, there are only 64 VLAN entries for HW VLAN
filter, and it leads to limit the number of VLANs up to 64 among PF and
VFs. For SDN/NFV case, we need to handle unlimited VLAN packets on VF.
In such case, every VLAN packet can be transmitted to each VF.

When we try to make VLAN devices on VF, the 65th VLAN registration fails
and never be able to receive a packet with that VLAN tag.
If we do the below command on VM, ethX.65 to ethX.100 cannot be created.
# for i in `seq 1 100`; do \
ip link add link ethX name ethX.$i type vlan id $i; done

There is a capability to disable HW VLAN filter and that makes all VLAN
tagged packets can be transmitted to every VFs. After VLAN filter stage,
unicast packets are transmitted to VF which has the MAC address same as
the transmitting packet.

With this patch and "disable_hw_vlan_filter=1", we can use unlimited
number of VLANs on VF.

Disabling HW VLAN filter breaks some NIC features such as DCB and FCoE.
DCB and FCoE are disabled when HW VLAN filter is disabled by this module
parameter.
Because of that reason, the administrator has to know that before turning
off HW VLAN filter.
You might also want to note that it makes the system susceptible to
broadcast/multicast storms since it eliminates any/all VLAN isolation.
So a broadcast or multicast packet on one VLAN is received on ALL
interfaces regardless of their VLAN configuration. In addition the
current VF driver is likely to just receive the packet as untagged, see
ixgbevf_process_skb_fields(). As a result one or two VFs can bring the
entire system to a crawl by saturating the PCIe bus via
broadcast/multicast traffic since there is nothing to prevent them from
talking to each other over VLANs that are no longer there.
that's right.

On the other hand, an untagged packet is not isolated,
doesn't it same broadcast/multicast storm on untagged network?

Yes, that is one of the reasons for VLANs. It provides isolation so that if you have two entities on the same network you won't have entity A able to talk to entity B. The problem is with VLAN promiscuous enabled if entity B is a VF it will see the traffic but has no way to know that it was VLAN tagged and a part of entity A's VLAN.


For the sake of backwards compatibility I would say that a feature like
this should be mutually exclusive with SR-IOV as well since it will
cause erratic behavior. The VF will receive requests from all VLANs
thinking the traffic is untagged, and then send replies back to VLAN 0
even though that isn't where the message originated.
Sorry, I couldn't catch the above part.
Could you explain a bit more?

thanks,
Hiroshi

Until the VF issue
is fixed this type of feature is a no-go.


The current behavior for a VF is that if it receives a VLAN that it didn't request it assumes it is operating in port VLAN mode. The problem is with your patch the VF will be receiving all traffic but have no idea which VLAN it came from. As a result it could be replying to multicast or broadcast requests on one VLAN with the wrong VLAN ID.

The VLAN behavior of the VF drivers will need to be fixed before something like that could be supported with ANY of the VFs. As such you will probably need to fix the VF driver in order to allow any of them to come online when VLAN filtering is disabled, as the driver will need to report the VLAN tag ID up to the stack.

- Alex

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/