netdev - RE: [RFC PATCH 00/13] Ultra Ethernet driver introduction

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Date: Wed, 26 Mar 2025 17:39:52 +0000
From: Sean Hefty <shefty@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
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Subject: RE: [RFC PATCH 00/13] Ultra Ethernet driver introduction

> > > Like I said already, I think Job needs to be a first class RDMA
> > > object that is used by all transports that have job semantics.
> >
> > How do you handle or expose device specific resource allocations or
> > restrictions, which may be needed?  Should a kernel 'RDMA job manager'
> > abstract device level resources?
> >
> > Consider a situation where a MR or MW should only be accessible by a
> > specific job.  When the MR is created, the device specific job
> > resource may be needed.  Should drivers need to query the job manager
> > to map some global object to a device specific resource?
> 
> I imagine for cases like that the job would be linked to the PD and then MR ->
> PD -> Job.
> 
> The kernel side would create any HW object for the job when the PD is created
> for a specific HW device.
> 
> The PD security semantic for the MR would be a little bit different in that the
> PD is more like a shared PD.

The PD is a problem, as it's not a transport function.  It's a hardware implementation component; one which may NOT exist for a UEC NIC.  (I know there are NICs which do not implement PDs and have secure RDMA transfers.)  I have a proposal to rework/redefine PDs to support a more general model, which I think will work for NICs that need a PD and ones that don't.  It can support MR -> PD -> Job, but I considered the PD -> job relationship as 1 to many.  I can't immediately think of a reason why a 1:1 'job-based PD' wouldn't work in theory.

It's challenging in that a UET endpoint (QP) may communicate with multiple jobs, and a MR may be accessible by a single job, all jobs, or only a few.

Basically, the RDMA PD model forces a HW implementation.  Some, but not all, NICs will implement this.  But in general, there's not a clean {PD, QP, MR, job} relationship.

- Sean