Re: [PATCH net-next v2 6/9] net: macsec: hardware offloading infrastructure

Hi Igor,

On Tue, Aug 13, 2019 at 04:18:40PM +0000, Igor Russkikh wrote:

On 13.08.2019 16:17, Andrew Lunn wrote:

quoted

On Tue, Aug 13, 2019 at 10:58:17AM +0200, Antoine Tenart wrote:

quoted

I think this question is linked to the use of a MACsec virtual interface
when using h/w offloading. The starting point for me was that I wanted
to reuse the data structures and the API exposed to the userspace by the
s/w implementation of MACsec. I then had two choices: keeping the exact
same interface for the user (having a virtual MACsec interface), or
registering the MACsec genl ops onto the real net devices (and making
the s/w implementation a virtual net dev and a provider of the MACsec
"offloading" ops).

The advantages of the first option were that nearly all the logic of the
s/w implementation could be kept and especially that it would be
transparent for the user to use both implementations of MACsec.

We have always talked about offloading operations to the hardware,
accelerating what the linux stack can do by making use of hardware
accelerators. The basic user API should not change because of
acceleration. Those are the general guidelines.

It would however be interesting to get comments from those who did the
software implementation and what they think of this architecture. I've
no personal experience with MACSec, so it is hard for me to say if the
current architecture makes sense when using accelerators.

In terms of overall concepts, I'd add the following:

1) With current implementation it's impossible to install SW macsec engine onto
the device which supports HW offload. That could be a strong limitation in
cases when user sees HW macsec offload is broken or work differently, and he/she
wants to replace it with SW one.
MACSec is a complex feature, and it may happen something is missing in HW.
Trivial example is 256bit encryption, which is not always a musthave in HW
implementations.

Agreed. I'm not sure it would be possible to have both used at the same
time but there should be a way to switch between the two
implementations. That is not supported for now, but I think that would
be a good thing, and can probably come later on.

2) I think, Antoine, its not totally true that otherwise the user macsec API
will be broken/changed. netlink api is the same, the only thing we may want to
add is an optional parameter to force selection of SW macsec engine.

I meant that we can either have a virtual net device representing the
MACsec feature and being the iface used to configure it, or we could
have it only when s/w MACsec is used. That to me is part of the "API",
or at least part of what's exposed to the user.

I'm also eager to hear from sw macsec users/devs on whats better here.

I'd like more comments as well :)

Thanks!
Antoine

-- 
Antoine Ténart, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com