From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D239C43603 for ; Thu, 12 Dec 2019 14:48:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E67F206A5 for ; Thu, 12 Dec 2019 14:48:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729803AbfLLOsv (ORCPT ); Thu, 12 Dec 2019 09:48:51 -0500 Received: from mail-ot1-f67.google.com ([209.85.210.67]:38885 "EHLO mail-ot1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729603AbfLLOsu (ORCPT ); Thu, 12 Dec 2019 09:48:50 -0500 Received: by mail-ot1-f67.google.com with SMTP id h20so2245082otn.5; Thu, 12 Dec 2019 06:48:50 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=voZVPNoSy4a8bMYdTcCablMq5CNO8vg9KUaW07IxqF0=; b=YwRTukMxntgOWx6/kVL9ZGvZBDrJZgnJlyHI9ZMaj0YrrVlNMLNKzkqSr4ISF4aq5i caxcomtk8t49UXVHqq9wbTGu5fEKfLWkK7HyeRjWP0uukat6YZEFHdHDe4cRnM/8mywo +wWE94qEVnqDYpAl1zAzCvVx/X0LQ2wTnbbj67NXQbSeycN4HFyxIBTR9TVnMRHgPgDa /o33OAATNQxxxubkDh3lhqtUiU7v6XX+vgg3R3YmQJL4joxLNZzjfjjIVFwYi1O+YirW 6eahBY2Cu0WzTmxDBtWP1VMT7E5ukt5MnViWU+XhBf1COeUoZq5bnbaWdFYqUiI07UrC zJdQ== X-Gm-Message-State: APjAAAVfXY0/4BbjFJHdS+J2hENLrfOka9xNEORAjF0ZGAHgHCw9z9sE 4TkxubRUpi3/o15DGyUHpGL7SvHQxdaewopCVLo= X-Google-Smtp-Source: APXvYqzkSI69hH3nkOuTuzoZ5DVB2dOkFajJLW18qhY+01LkXcbQ2mLFjldvRytBCaRPVXRqDE7Vp+g1Jzj78r5O+Hc= X-Received: by 2002:a9d:dc1:: with SMTP id 59mr8660446ots.250.1576162129675; Thu, 12 Dec 2019 06:48:49 -0800 (PST) MIME-Version: 1.0 References: <20191127084253.16356-1-geert+renesas@glider.be> <20191127084253.16356-7-geert+renesas@glider.be> In-Reply-To: From: Geert Uytterhoeven Date: Thu, 12 Dec 2019 15:48:38 +0100 Message-ID: Subject: Re: [PATCH v3 6/7] docs: gpio: Add GPIO Aggregator/Repeater documentation To: Linus Walleij Cc: Geert Uytterhoeven , Bartosz Golaszewski , Jonathan Corbet , Rob Herring , Mark Rutland , Harish Jenny K N , Eugeniu Rosca , Alexander Graf , Peter Maydell , Paolo Bonzini , Phil Reid , Marc Zyngier , Christoffer Dall , Magnus Damm , "open list:GPIO SUBSYSTEM" , Linux Doc Mailing List , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Linux-Renesas , "linux-kernel@vger.kernel.org" , QEMU Developers Content-Type: text/plain; charset="UTF-8" Sender: linux-renesas-soc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-renesas-soc@vger.kernel.org Hi Linus, On Thu, Dec 12, 2019 at 3:42 PM Linus Walleij wrote: > On Wed, Nov 27, 2019 at 9:43 AM Geert Uytterhoeven > 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. 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