From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>,
Bartosz Golaszewski <bgolaszewski@baylibre.com>,
Jonathan Corbet <corbet@lwn.net>,
Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Harish Jenny K N <harish_kandiga@mentor.com>,
Eugeniu Rosca <erosca@de.adit-jv.com>,
Alexander Graf <graf@amazon.com>,
Peter Maydell <peter.maydell@linaro.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Phil Reid <preid@electromag.com.au>,
Marc Zyngier <marc.zyngier@arm.com>,
Christoffer Dall <christoffer.dall@arm.com>,
Magnus Damm <magnus.damm@gmail.com>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
Linux Doc Mailing List <linux-doc@vger.kernel.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [PATCH v3 6/7] docs: gpio: Add GPIO Aggregator/Repeater documentation
Date: Mon, 6 Jan 2020 09:06:53 +0100 [thread overview]
Message-ID: <CAMuHMdWZ7Wh9rq7SGt7edgCXL1e5UwtSUfxLc0exHa-TEB=W5w@mail.gmail.com> (raw)
In-Reply-To: <CACRpkdZwos9Dtt9E3OkxWf4rqMALNTge5NGduzGm-7MhQyLZuQ@mail.gmail.com>
Hi Linus,
On Sat, Jan 4, 2020 at 1:21 AM Linus Walleij <linus.walleij@linaro.org> wrote:
> On Thu, Dec 12, 2019 at 3:48 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Thu, Dec 12, 2019 at 3:42 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> > > On Wed, Nov 27, 2019 at 9:43 AM Geert Uytterhoeven
> > > <geert+renesas@glider.be> wrote:
> > > > +The GPIO Aggregator allows access control for individual GPIOs, by aggregating
> > > > +them into a new gpio_chip, which can be assigned to a group or user using
> > > > +standard UNIX file ownership and permissions. Furthermore, this simplifies and
> > > > +hardens exporting GPIOs to a virtual machine, as the VM can just grab the full
> > > > +GPIO controller, and no longer needs to care about which GPIOs to grab and
> > > > +which not, reducing the attack surface.
> > > > +
> > > > +Aggregated GPIO controllers are instantiated and destroyed by writing to
> > > > +write-only attribute files in sysfs.
> > >
> > > I suppose virtual machines will have a lengthy config file where
> > > they specify which GPIO lines to pick and use for their GPIO
> > > aggregator, and that will all be fine, the VM starts and the aggregator
> > > is there and we can start executing.
> > >
> > > I would perhaps point out a weakness as with all sysfs and with the current
> > > gpio sysfs: if a process creates an aggregator device, and then that
> > > process crashes, what happens when you try to restart the process and
> > > run e.g. your VM again?
> > >
> > > Time for a hard reboot? Or should we add some design guidelines for
> > > these machines so that they can cleanly tear down aggregators
> > > previously created by the crashed VM?
> >
> > No, the VM does not create the aggregator.
> >
> > The idea is for the user to create one or more aggregators, set up
> > permissions on /dev/gpiochipX, and launch the VM, passing the aggregated
> > /dev/gpiochipX as parameters.
> > If the VM crashes, just launch it again.
> >
> > Destroying the aggregators is a manual and independent process, after
> > the VM has exited.
>
> I'm thinking about someone making some industrial application for some
> control of a machinery say a robotic arm.
>
> And do make sure this VM is only controlling these GPIOs related to
> this robotic arm, they create a GPIO aggregator. And we care about
> cases like that since we provide this security argument.
>
> Surely that machine will be rebooted.
>
> Surely they don't have a printed paper with all the commands lying
> at the console, and asking whoever powers it back on to manually
> type it all in again. That feels a bit 1981.
>
> So they will have a script for this I suppose. Possibly in some
> initscript so it is set up on boot. And this script echos stuff
> all over the place to set up the aggregator.
>
> Is this the use case you're thinking of?
Exactly.
And they can configure that by echoing the GPIO specifiers to
/sys/bus/platform/drivers/gpio-aggregator/new_device.
If their system has DT, another option is to describe the device in DT,
and add its compatible value to gpio_aggregator_dt_ids[], cfr. the
frobnicator example.
> I just like to have the whole picture here.
Sure. If anything is still unclear, please let me know!
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2020-01-06 8:07 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-27 8:42 [PATCH v3 0/7] gpio: Add GPIO Aggregator/Repeater Geert Uytterhoeven
2019-11-27 8:42 ` [PATCH v3 1/7] gpiolib: Add GPIOCHIP_NAME definition Geert Uytterhoeven
2019-11-28 3:38 ` Ulrich Hecht
2019-12-02 21:17 ` Eugeniu Rosca
2019-12-12 10:37 ` Linus Walleij
2019-11-27 8:42 ` [PATCH v3 2/7] gpiolib: Add support for gpiochipN-based table lookup Geert Uytterhoeven
2019-11-28 3:38 ` Ulrich Hecht
2019-12-12 13:20 ` Linus Walleij
2019-12-12 13:33 ` Geert Uytterhoeven
2019-12-12 14:36 ` Linus Walleij
2019-11-27 8:42 ` [PATCH v3 3/7] gpiolib: Add support for GPIO line " Geert Uytterhoeven
2019-11-28 3:39 ` Ulrich Hecht
2019-12-12 13:40 ` Linus Walleij
2019-11-27 8:42 ` [PATCH v3 4/7] dt-bindings: gpio: Add gpio-repeater bindings Geert Uytterhoeven
2019-11-28 3:39 ` Ulrich Hecht
2019-12-03 5:51 ` Harish Jenny K N
2019-12-05 21:06 ` Rob Herring
2019-12-06 9:17 ` Geert Uytterhoeven
2019-12-06 15:03 ` Rob Herring
2020-01-06 8:12 ` Geert Uytterhoeven
2020-01-07 9:22 ` Harish Jenny K N
2020-01-16 5:09 ` Harish Jenny K N
2019-11-27 8:42 ` [PATCH v3 5/7] gpio: Add GPIO Aggregator/Repeater driver Geert Uytterhoeven
2019-11-27 14:15 ` Eugeniu Rosca
2019-11-27 14:33 ` Geert Uytterhoeven
2019-11-28 3:40 ` Ulrich Hecht
2019-12-03 5:42 ` Harish Jenny K N
2019-12-03 8:17 ` Geert Uytterhoeven
2019-12-03 8:51 ` Harish Jenny K N
2019-12-03 10:51 ` Eugeniu Rosca
2020-01-09 13:35 ` Geert Uytterhoeven
2020-01-09 13:49 ` Eugeniu Rosca
2019-12-12 14:34 ` Linus Walleij
2019-12-12 15:24 ` Geert Uytterhoeven
2020-01-04 0:38 ` Linus Walleij
2020-01-06 8:23 ` Geert Uytterhoeven
2020-01-08 23:12 ` Linus Walleij
2019-11-27 8:42 ` [PATCH v3 6/7] docs: gpio: Add GPIO Aggregator/Repeater documentation Geert Uytterhoeven
2019-11-28 3:41 ` Ulrich Hecht
2019-12-12 14:42 ` Linus Walleij
2019-12-12 14:48 ` Geert Uytterhoeven
2020-01-04 0:21 ` Linus Walleij
2020-01-06 8:06 ` Geert Uytterhoeven [this message]
2019-11-27 8:42 ` [PATCH v3 7/7] MAINTAINERS: Add GPIO Aggregator/Repeater section Geert Uytterhoeven
2019-12-03 5:38 ` Harish Jenny K N
2020-01-18 1:46 ` [PATCH v3 0/7] gpio: Add GPIO Aggregator/Repeater Eugeniu Rosca
2020-01-20 9:33 ` Geert Uytterhoeven
2020-01-20 12:14 ` Eugeniu Rosca
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