Re: [virtio-dev] Re: [virtio-comment] Re: [PATCH v12] virtio-net: support inner header hash

[Heng Qi <hengqi@linux.alibaba.com>]

å 2023/4/14 äå5:43, Michael S. Tsirkin åé:
> On Thu, Apr 13, 2023 at 07:03:26PM +0800, Heng Qi wrote:
> > > >  Â For example, when the packets of certain
> > > > +tunnels are spread across multiple receive queues, these receive
> > > > queues may have an unbalanced
> > > > +amount of packets. This can cause a specific receive queue to
> > > > become full, resulting in packet loss.
> > >
> > > We have many places that can lead to packet dropping. For example, the
> > > automatic steering is best effort. I tend to avoid mentioning things
> > > like this.
> > Ok. And Michael what do you think about this?
>
> I think this text did not do a great job explaining the
> security aspect. Here's a better, shorter explanation:
>
> 	It is often an expectation of users that a tunnel isolates the external
> 	network from the internal one. By completely ignoring entropy in the
> 	external header and replacing it with entropy from the internal header,
> 	for hash calculations, this expectation might be violated to a certain
> 	extent, depending on how the hash is used. When the hash use is limited
> 	to RSS queue selection, the effect will likely be limited to ability of
> 	users inside the tunnel to cause packet drops in multiple queues (as
> 	opposed to a single queue without the feature).

Sure. Will do in the v13.

> > > > +
> > > > +Possible mitigations:
> > > > +\begin{itemize}
> > > > +\item Use a tool with good forwarding performance to keep the
> > > > receive queue from filling up.
> > > > +\item If the QoS is unavailable, the driver can set
> > > > \field{hash_tunnel_types} to VIRTIO_NET_HASH_TUNNEL_TYPE_NONE
> > > > +ÂÂÂÂÂ to disable inner header hash for encapsulated packets.
> > > > +\item Choose a hash key that can avoid queue collisions.
> > > > +\item Perform appropriate QoS before packets consume the receive
> > > > buffers of the receive queues.
> > > > +\end{itemize}
> > > > +
> > > > +The limitations mentioned above exist with/without the inner header
> > > > hash.
> > >
> > > This conflicts with the tile "Tunnel QoS limitation" which readers may
> > > think it happens only for tunnel.
> > Perhaps a "QoS Advices" is better?
> Plural of "advice" is "advice" not "advices".

My fault.ð

> This advice is somewhat bogus though.
>
> The point I keep trying to make is that this:
>
> 	Choose a hash key that can avoid queue collisions.
>
> is impossible with the feature and possible without.

I don't think so, the outer headers also has corresponding entropy for 
different streams.

Thanks.

> This was the whole reason I asked for a security
> considerations sections.
>
>
> > Thanks!
> >
> > > Thanks
> > >
> > >
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