Re: [PATCH v9] virtio-net: support inner header hash

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Feb 27, 2023 at 04:35:09PM +0800, Jason Wang wrote:
> On Mon, Feb 27, 2023 at 3:39 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Mon, Feb 27, 2023 at 12:07:17PM +0800, Jason Wang wrote:
> > > Btw, this kind of 1:1 hash features seems not scalable and flexible.
> > > It requires an endless extension on bits/fields. Modern NICs allow the
> > > user to customize the hash calculation, for virtio-net we can allow to
> > > use eBPF program to classify the packets. It seems to be more flexible
> > > and scalable and there's almost no maintain burden in the spec (only
> > > bytecode is required, no need any fancy features/interactions like
> > > maps), easy to be migrated etc.
> > >
> > > Prototype is also easy, tun/tap had an eBPF classifier for years.
> > >
> > > Thanks
> >
> > Yea BPF offload would be great to have. We have been discussing it for
> > years though - security issues keep blocking it. *Maybe* it's finally
> > going to be there but I'm not going to block this work waiting for BPF
> > offload.  And easily migrated is what BPF is not.
> 
> Just to make sure we're at the same page. I meant to find a way to
> allow the driver/user to fully customize what it wants to
> hash/classify. Similar technologies which is based on private solution
> has been used by some vendors, which allow user to customize the
> classifier[1]
> 
> ePBF looks like a good open-source solution candidate for this (there
> could be others). But there could be many kinds of eBPF programs that
> could be offloaded. One famous one is XDP which requires many features
> other than the bytecode/VM like map access, tailcall. Starting from
> such a complicated type is hard. Instead, we can start from a simple
> type, that is the eBPF classifier. All it needs is to pass the
> bytecode to the device, the device can choose to run it or compile it
> to what it can understand for classifying. We don't need maps, tail
> calls and other features.

Until people start asking exactly for maps because they want
state for their classifier? And it makes sense - if you want
e.g. load balancing you need stats which needs maps.

> We don't need to worry about the security
> because of its simplicity: the eBPF program is only in charge of doing
> classification, no other interactions with the driver and packet
> modification is prohibited. The feature is limited only to the
> VM/bytecode abstraction itself.
> 
> What's more, it's a good first step to achieve full eBPF offloading in
> the future.
> 
> Thanks
> 
> [1] https://www.intel.com/content/www/us/en/architecture-and-technology/ethernet/dynamic-device-personalization-brief.html

Dave seems to have nacked this approach, no?

> >
> > --
> > MST
> >