linux-kernel - Re: [PATCH v1] driver: base: Add driver filter support

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Date:   Thu, 5 Aug 2021 12:52:30 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v1] driver: base: Add driver filter support

[ add Jonathan ]

On Thu, Aug 5, 2021 at 12:28 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Thu, Aug 05, 2021 at 12:18:12PM -0700, Dan Williams wrote:
> > On Thu, Aug 5, 2021 at 12:12 PM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Thu, Aug 05, 2021 at 11:53:52AM -0700, Kuppuswamy, Sathyanarayanan wrote:
> > > > I am not sure how USB and Thunderbolt "authorzied" model works. But I
> > > > don't think it prevents built-in driver probes during kernel boot right?
> > >
> > > Yes it does.
> > >
> > > Again Intel created this framework well over a decade ago for busses
> > > that it deemed that it did not want to "trust" to instantly probe
> > > drivers for and made it part of the Wireless USB specification.
> > >
> > > Then Intel went and added the same framework to Thunderbolt for the same
> > > reason.
> > >
> > > To ignore this work is quite odd, you might want to talk to your
> > > coworkers...
> >
> > Sometimes we need upstream to connect us wayward drones back into the
> > hive mind. Forgive me for not immediately recognizing that the
> > existing 'authorized' mechanisms might be repurposed for this use
> > case.
>
> Not your fault, I'm more amazed that Andi doesn't remember this, he's
> been around longer :)
>

In the driver core? No, not so much, and I do remember it flying by,
just did not connect the dots. In fact, it had just gone upstream when
you and I had that thread about blocking PCI drivers [1], September
2017 vs June 2017 when the Thunderbolt connection manager was merged.
There was no internal review process back then so I failed to
internalize its implications for this TDX filter. You had taken the
time to review it in a way that I had not.

> But the first instinct should not be "let's go add a new feature", but
> rather, "how has this problem been solved by others first" because,
> really, this is not a new issue at all.  You should not rely on just me
> to point out existing kernel features, we do have documentation you
> know...

I have added, "review driver core attribute proposal for duplication
of bus-local capabilities" to my review checklist.

The good news is I think this generic authorization support in the
core may answer one of Jonathan's questions about how to integrate PCI
SPDM/CMA support [2].

[1]: https://lore.kernel.org/lkml/20170928090901.GC12599@kroah.com/
[2]: https://lore.kernel.org/r/20210804161839.3492053-1-Jonathan.Cameron@huawei.com