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 AC94CC43603 for ; Thu, 12 Dec 2019 14:49:38 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8687121655 for ; Thu, 12 Dec 2019 14:49:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8687121655 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-m68k.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:60898 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ifPmb-0000VZ-Kg for qemu-devel@archiver.kernel.org; Thu, 12 Dec 2019 09:49:37 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:35919) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ifPlt-00005R-OS for qemu-devel@nongnu.org; Thu, 12 Dec 2019 09:48:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ifPlr-000774-HC for qemu-devel@nongnu.org; Thu, 12 Dec 2019 09:48:53 -0500 Received: from mail-ot1-f67.google.com ([209.85.210.67]:35207) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1ifPlr-00074S-Az for qemu-devel@nongnu.org; Thu, 12 Dec 2019 09:48:51 -0500 Received: by mail-ot1-f67.google.com with SMTP id o9so2249602ote.2 for ; 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=B8AR3oqVBR8n6jBYVr6V4/wE1vVUDly0e9Ty8Na2fFY37pQYBVwa9c/RZAuJSy5hFe UAK+nFPhlOksp1p5YALq31lf8DcExKz0y2imdw2f6HDUfu2FWS4AIsGsmnYlzeoEn9Ji xdd2pjfsmP9JcV82WcUMuEX8YHPBJdTnuW9uzQVGrRu/ncYHLnPgfIeM5WGj0QCKlwxy d3iF7ZlpisSBpBY0T7j3rRvdSHA+dO9rwr/FlEf1PLMZwOVtJJRpDSdkqOye8Lr/7nGq AIz3C9XqTyeG2jsszii7t56i54XkzyQyyspinrlRHKvoyj3gph38TmPvFCQWST0O+k6X Hnrw== X-Gm-Message-State: APjAAAVD0BdRjOcmjJpSxmYlzdZt0wlSBlnlPXZHp9RO7vGgHqlkGez/ 1Lh9T2dfIkpjPL5PInkhGPS77Z3FPzdeWipLRTU= 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 Content-Type: text/plain; charset="UTF-8" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.85.210.67 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Peter Maydell , QEMU Developers , Phil Reid , Geert Uytterhoeven , Jonathan Corbet , Marc Zyngier , "open list:GPIO SUBSYSTEM" , Linux Doc Mailing List , Magnus Damm , Christoffer Dall , "linux-kernel@vger.kernel.org" , Linux-Renesas , Bartosz Golaszewski , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Rob Herring , Harish Jenny K N , Paolo Bonzini , Alexander Graf , Eugeniu Rosca Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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