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From: Linus Walleij <linus.walleij@linaro.org>
To: Geert Uytterhoeven <geert@linux-m68k.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: Sat, 4 Jan 2020 01:21:27 +0100
Message-ID: <CACRpkdZwos9Dtt9E3OkxWf4rqMALNTge5NGduzGm-7MhQyLZuQ@mail.gmail.com> (raw)
In-Reply-To: <CAMuHMdV+Ww5Y9G7+bS-SyHtm4dC89V37yuaYvrS3kYW=PRTkFA@mail.gmail.com>

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?

I just like to have the whole picture here.

Yours,
Linus Walleij

  reply index

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 [this message]
2020-01-06  8:06         ` Geert Uytterhoeven
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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