Re: [net-next-2.6 PATCH 0/3 RFC] macvlan: MAC Address filtering support for passthru mode

On 9/8/11 10:42 AM, "Sridhar Samudrala" [off-list ref] wrote:

On Thu, 2011-09-08 at 09:19 -0700, Roopa Prabhu wrote:

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On 9/8/11 4:08 AM, "Michael S. Tsirkin" [off-list ref] wrote:

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On Wed, Sep 07, 2011 at 10:20:28PM -0700, Roopa Prabhu wrote:

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On 9/7/11 5:34 AM, "Michael S. Tsirkin" [off-list ref] wrote:

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On Tue, Sep 06, 2011 at 03:35:40PM -0700, Roopa Prabhu wrote:

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This patch is an attempt at providing address filtering support for
macvtap
devices in PASSTHRU mode. Its still a work in progress.
Briefly tested for basic functionality. Wanted to get some feedback on
the
direction before proceeding.

Good work, thanks.

Thanks.

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I have hopefully CC'ed all concerned people.

kvm crowd might also be interested.
Try using ./scripts/get_maintainer.pl as well.

Thanks for the tip. Expanded CC list a bit more.

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PASSTHRU mode today sets the lowerdev in promiscous mode. In PASSTHRU
mode
there is a 1-1 mapping between macvtap device and physical nic or VF. And
all
filtering is done in lowerdev hw. The lowerdev does not need to be in
promiscous mode as long as the guest filters are passed down to the
lowerdev.
This patch tries to remove the need for putting the lowerdev in
promiscous
mode. 
I have also referred to the thread below where TUNSETTXFILTER was
mentioned
in 
this context:
 http://patchwork.ozlabs.org/patch/69297/

This patch basically passes the addresses got by TUNSETTXFILTER to
macvlan
lowerdev.

I have looked at previous work and discussions on this for qemu-kvm
by Michael Tsirkin, Alex Williamson and Dragos Tatulea
http://patchwork.ozlabs.org/patch/78595/
http://patchwork.ozlabs.org/patch/47160/
https://patchwork.kernel.org/patch/474481/

Redhat bugzilla by Michael Tsirkin:
https://bugzilla.redhat.com/show_bug.cgi?id=655013

I used Michael's qemu-kvm patch for testing the changes with KVM

I would like to cover both MAC and vlan filtering in this work.

Open Questions/Issues:
- There is a need for vlan filtering to complete the patch. It will
require
  a new tap ioctl cmd for vlans.
  Some ideas on this are:

  a) TUNSETVLANFILTER: This will entail we send the whole vlan bitmap
filter
(similar to tun_filter for addresses). Passing the vlan id's to lower
device will mean going thru the whole list of vlans every time.

  OR

  b) TUNSETVLAN with vlan id and flag to set/unset

  Does option 'b' sound ok ?

- In this implementation we make the macvlan address list same as the
address
  list that came in the filter with TUNSETTXFILTER. This will not cover
cases
  where the macvlan device needs to have other addresses that are not
  necessarily in the filter. Is this a problem ?

What cases do you have in mind?

This patch targets only macvlan PASSTHRU mode and for PASSTHRU mode I don't
see a problem with uc/mc address list being the same in all the stacked
netdevs in the path. I called that out above to make sure I was not missing
any case in PASSTHRU mode where this might be invalid. Otherwise I don't
see
a problem in the simple PASSTHRU use case this patch supports.

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- The patch currently only supports passing of IFF_PROMISC and
IFF_MULTICAST
filter flags to lowerdev

This patch series implements the following
01/3 - macvlan: Add support for unicast filtering in macvlan
02/3 - macvlan: Add function to set addr filter on lower device in
passthru
mode
03/3 - macvtap: Add support for TUNSETTXFILTER

Please comment. Thanks.

Signed-off-by: Roopa Prabhu <redacted>
Signed-off-by: Christian Benvenuti <redacted>
Signed-off-by: David Wang <redacted>

The security isn't lower than with promisc, so I don't see
a problem with this as such.

There are more features we'll want down the road though,
so let's see whether the interface will be able to
satisfy them in a backwards compatible way before we
set it in stone. Here's what I came up with:

How will the filtering table be partitioned within guests?

Since this patch supports macvlan PASSTHRU mode only, in which the lower
device has 1-1 mapping to the guest nic, it does not require any
partitioning of filtering table within guests. Unless I missed
understanding
something. 
If the lower device were being shared by multiple guest network interfaces
(non PASSTHRU mode), only then we will need to maintain separate filter
tables for each guest network interface in macvlan and forward the pkt to
respective guest interface after a filter lookup. This could affect
performance too I think.

Not with hardware filtering support. Which is where we'd need to
partition the host nic mac table between guests.

I need to understand this more. In non passthru case when a VF or physical
nic is shared between guests, the nic does not really know about the guests,
so I was thinking we do the same thing as we do for the passthru case (ie
send all the address filters from macvlan to the physical nic). So at the
hardware, filtering is done for all guests sharing the nic. But if we want
each virtio-net nic or guest to get exactly what it asked for
macvlan/macvtap needs to maintain a copy of each guest filter and do a
lookup and send only the requested traffic to the guest. Here is the
performance hit that I was seeing. Please see my next comment for further
details. 

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I chose to support PASSTHRU Mode only at first because its simpler and all
code additions are in control path only.

I agree. It would be a bit silly to have a dedicated interface
for passthough and a completely separate one for
non passthrough.

Agree. The reason I did not focus on non-passthru case in the initial
version was because I was thinking things to do in the non-passthru case
will be just add-ons to the passthru case. But true Better to flush out the
non-pasthru case details.

After dwelling on this a bit more how about the below:

Phase 1: Goal: Enable hardware filtering for all macvlan modes
    - In macvlan passthru mode the single guest virtio-nic connected will
receive traffic that he requested for

Currently the guest receives all the packets seen on the interface as it
is put in promiscuous mode. With your patch it only sees the packets
that he requested for. Have you tried creating a macvlan interface on
top of the guest virtio-net interface? Is the new mac address propagated
all the way to the host nic?

Yes I have tried this and it works. The mac address gets propagated to the
physical nic.

I think the main usecase for passthru mode is to assign a SR-IOV VF to
a single guest.

Yes and for the passthru usecase this patch should be enough to enable
filtering in hw (eventually like I indicated before I need to fix vlan
filtering too).

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    - In macvlan non-passthru mode all guest virtio-nics sharing the
      physical nic will see all other guest traffic
      but the filtering at guest virtio-nic will make sure each guest
      eventually sees traffic he asked for. This is still better than
putting the physical nic in promiscuous mode.

With the default macvlan mode (vepa), i think each guest will only see
its own traffic. But currently adding a secondary mac address on a guest
will not work as it is not propagated all the way down to the host.

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(This is mainly what my patch does...but will need to remove the passthru
check and see if there are any thing else needed for non-passthru case)


Phase 2: Goal: Enable filtering at macvlan so that each guest virtio-nic
receives only what he requested for.
    - In this case, in addition to pushing the filters down to the physical
nic we will have to maintain the same filter in macvlan and do a filter
lookup before forwarding the traffic to a virtio-nic.

But I am thinking phase 2 might be redundant given virtio-nic already does
filtering for the guest. In which case we might not need phase 2 at all. I
might have been over complicating things.

I think filtering at macvlan will be more efficient than replicating all
the packets to all the guest virtio-nics.

True. This usecase is for non-passthru and I think it will require some
performance testing for all modes too. Could be a phase II patch with the
current patch only enabling filtering in hw.

Thanks for the comments,
Roopa