Message-ID: <F6FB0E698C9B3143BDF729DF22286646912EFEC4@ORSMSX110.amr.corp.intel.com>
Date:	Tue, 12 May 2015 00:21:28 +0000
From:	"Skidmore, Donald C" <donald.c.skidmore@...el.com>
To:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>,
	Or Gerlitz <gerlitz.or@...il.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
CC:	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"nhorman@...hat.com" <nhorman@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>,
	"jogreene@...hat.com" <jogreene@...hat.com>,
	"Choi, Sy Jong" <sy.jong.choi@...el.com>,
	Edward Cree <ecree@...arflare.com>,
	Rony Efraim <ronye@...lanox.com>
Subject: RE: [net-next 07/11] if_link: Add VF multicast promiscuous control



> -----Original Message-----
> From: Hiroshi Shimamoto [mailto:h-shimamoto@...jp.nec.com]
> Sent: Monday, May 11, 2015 4:55 PM
> To: Skidmore, Donald C; Or Gerlitz; Kirsher, Jeffrey T
> Cc: David Miller; Linux Netdev List; nhorman@...hat.com;
> sassmann@...hat.com; jogreene@...hat.com; Choi, Sy Jong; Edward Cree;
> Rony Efraim
> Subject: RE: [net-next 07/11] if_link: Add VF multicast promiscuous control
> 
> > > > -----Original Message-----
> > > > From: Hiroshi Shimamoto [mailto:h-shimamoto@...jp.nec.com]
> > > > Sent: Wednesday, May 06, 2015 10:55 PM
> > > > To: Skidmore, Donald C; Or Gerlitz; Kirsher, Jeffrey T
> > > > Cc: David Miller; Linux Netdev List; nhorman@...hat.com;
> > > > sassmann@...hat.com; jogreene@...hat.com; Choi, Sy Jong; Edward
> > > > Cree; Rony Efraim
> > > > Subject: RE: [net-next 07/11] if_link: Add VF multicast
> > > > promiscuous control
> > > >
> > > > > > -----Original Message-----
> > > > > > From: Or Gerlitz [mailto:gerlitz.or@...il.com]
> > > > > > Sent: Sunday, May 03, 2015 7:16 AM
> > > > > > To: Kirsher, Jeffrey T
> > > > > > Cc: David Miller; Hiroshi Shimamoto; Linux Netdev List;
> > > > > > nhorman@...hat.com; sassmann@...hat.com;
> jogreene@...hat.com;
> > > > Choi,
> > > > > > Sy Jong; Edward Cree; Skidmore, Donald C; Rony Efraim
> > > > > > Subject: Re: [net-next 07/11] if_link: Add VF multicast
> > > > > > promiscuous control
> > > > > >
> > > > > > On Sat, May 2, 2015 at 1:42 PM, Jeff Kirsher
> > > > > > <jeffrey.t.kirsher@...el.com>
> > > > > > wrote:
> > > > > > > From: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
> > > > > > >
> > > > > > > Add netlink directives and ndo entry to allow VF multicast
> > > > > > > promiscuous
> > > > > > mode.
> > > > > > >
> > > > > > > This controls the permission to enter VF multicast promiscuous
> mode.
> > > > > > > The administrator will dedicatedly allow multicast promiscuous per
> VF.
> > > > > > >
> > > > > > > When the VF is under multicast promiscuous mode, all
> > > > > > > multicast packets are sent to the VF.
> > > > > > >
> > > > > > > Don't allow VF multicast promiscuous if the VM isn't fully trusted.
> > > > > >
> > > > > > Guys,
> > > > > >
> > > > > > I don't think the discussion we held in the past [1] on the
> > > > > > matter actually converged. Few open points that came up while
> > > > > > debating it internally with
> > > > > > Rony:
> > > > > >
> > > > > > 1. maybe what we we actually want here an API that states a VF
> > > > > > to be privileged/trusted and then we can over load the feature
> > > > > > set of being
> > > > such?
> > > > >
> > > > > I suggested this originally, but there was push back as it was
> > > > > thought too
> > > > generic as the definition of what being a "trusted"
> > > > > vendor would differ from driver to driver.  Personally I still
> > > > > like the idea of
> > > > having one mode saying that we "trust"
> > > > > a given VF.  Then that VF can request whatever it support it
> > > > > wants from the PF regardless of possible negative impact on other
> VF's.
> > > > > What is possible to support would then be left to the interface
> > > > > between the VF and PF.  This of course would be dependent on
> > > > > what the
> > > > given HW could support and would mean this mode would mean
> > > > different things for different adapters and I do see why some
> > > > might see this as a concern.
> > > >
> > > > The point is granularity, right?
> > > > Allow everything or allow subset of features.
> > >
> > > Nice way to sum it up.  The trick being with the subset of features path is
> not all hardware can/will support everything.
> > > Also I worry about worry about the feature list growing requiring
> > > more and more nobs on the PF to allow/disallow granular behavior
> > > that could brake VF isolation.  With a simple hint to the PF that a given VF
> is "trusted" would allow all that complexity to be contained in the mailbox
> protocol between the PF/VF.
> > >
> > > All that said I realize others are concerned with the ambiguousness
> > > of such a field and can certainly live with your implementation.
> >
> > I see, it seems better to have a single knob which indicates "trust
> > this VF" and PF will allow requests which might hurt performance or
> > security from trusted VF, instead of creating a knob for multicast
> promiscuous, a knob for feature X and so on.
> >
> > I will make a patch to implement that "trusted knob" instead of allowing
> MC promiscuous.
> > Is there any comment?
> 
> Any comments?
> Is that the way to go ahead this series?
> 
> thanks,
> Hiroshi

Clearly I am ok with the idea.  :) 

If the change isn't too difficult to implement, maybe just submit the path.  That will most likely get more attention.

Thanks,
-Don <donald.c.skidmore@...el.com>

> 
> 
> >
> > >
> > > >
> > > > >
> > > > > >
> > > > > > 2. the suggested API only allows either unlimited number of
> > > > > > mulicast groups per VF or limited number, both numbers are
> > > > > > vendor dependent,
> > > > right?
> > > > > > maybe what we need for this specific matter is specifying how
> > > > > > many multicast groups are allowed for a VF?
> > > > >
> > > > > I believe the idea behind this interface was that it would allow
> > > > > VF's to request unlimited multicast group as opposed to the
> > > > > current behavior of each adapter offering some limited number.
> > > > > This limit is of course defined by a given adapters HW/SW
> > > > > limitations.  Up until now you could keep asking for new
> > > > > multicast until the PF replied with an error.  So we never
> > > > > really exported this information before.  This new
> > > > mode just allows us to never reach the point that the PF would
> > > > deny a VF request to join a MC group.  Seems to me that an
> > > > additional interface to provide the max number of supported
> > > > multicast groups would be new functionality that could be
> > > > independent of this patch and in fact could exist even without this
> patch.
> > > > > Or am I missing what you're asking for here. :)
> > > >
> > > > I think that the current limitation of multicast on ixgbevf comes
> > > > from the implementation of mailbox API between VF and PF which has
> 32 words.
> > > >
> > >
> > > In the end the limit on number of MC groups, if you don't use
> promiscuous mode, is the size of the multicast table array.
> > > We could be sharing this table better between all users rather than
> > > the arbitrary limit, but you would hit a hard limit due to the size of the
> table.
> >
> > Just to clarify the current implementation, I think there is no hard limit of
> MC address.
> > The ixgbe driver uses the MTA (multicast table array) and the MTA is
> > shared among all VFs. VF requests to register 30 multicast address hash
> values at most and PF will set the corresponding bit in the MTA.
> > When multicast packet comes in, NIC checks the MTA bit and transmit
> > the packet every VF. 82599 uses the
> > 12 bits hash value of MC address and there is the MTA which is 4096
> > bits array, the MTA covers all MC address to filter. I think if all bits on in the
> MTA, it means that no MC packet is dropped.
> >
> > thanks,
> > Hiroshi
> >
> > >
> > > > By the way, our requirement is to make VF promiscuous mode for
> > > > SDN/NFV usage.
> > > > And there is a feature to enable in HW, we'd like to use it.
> > > > I know there is a possibility of performance degradation.
> > > >
> > > > thanks,
> > > > Hiroshi
> > >
> > > I think your method is the way to go, in that if you ask for more
> > > than we allow per VF and the PF has this ability enabled we just put
> > > the VF into multicast promiscuous mode.  However I don't see the
> > > advantage of having an interface to tell how many groups need to be
> > > requested before this happens.  If you were worried about the
> > > performance degradation of
> > entering
> > > promiscuous multicast don't allow it in the PF, which of course will be the
> default.
> > >
> > > Thanks,
> > > -Don Skidmore <donald.c.skidmore@...el.com>
> > >
> > >

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