From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751637AbaIJO6U (ORCPT ); Wed, 10 Sep 2014 10:58:20 -0400 Received: from smtp.codeaurora.org ([198.145.11.231]:59122 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750770AbaIJO6S (ORCPT ); Wed, 10 Sep 2014 10:58:18 -0400 Message-ID: <54106707.4010006@codeaurora.org> Date: Wed, 10 Sep 2014 10:58:15 -0400 From: Christopher Covington User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130106 Thunderbird/17.0.2 MIME-Version: 1.0 To: Doug Anderson CC: Mark Rutland , Lorenzo Pieralisi , Russell King , Catalin Marinas , Daniel Lezcano , Stephen Boyd , "linux-kernel@vger.kernel.org" , Will Deacon , Sudeep Holla , Olof Johansson , Thomas Gleixner , Sonny Rao , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH] clocksource: arch_timer: Fix code to use physical timers when requested References: <1409173419-13076-1-git-send-email-sonnyrao@chromium.org> <53FE5B09.2020403@codeaurora.org> <53FE7E3B.1010500@codeaurora.org> <20140828093505.GC14650@leverpostej> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/05/2014 06:11 PM, Doug Anderson wrote: > Mark, > > On Thu, Aug 28, 2014 at 2:35 AM, Mark Rutland wrote: >> Not if you boot Linux at hyp, as we've recommended for this precise >> reason. That doesn't fix other things like CNTFRQ if the secure >> initialisation doesn't poke that, however. > > I'll freely admit that I'm out of my league and out of my comfort zone > here, but... > > In the theory that firmware ought to be as minimal as possible > (because it's hard to update and hard to keep in sync with kernel > versions), it seems like firmware ought to start the kernel out in as > permissive mode as it's willing to provide, right? > > If the kernel is started out as permissive as possible then it can do > anything it needs to. Future versions of the kernel can be > implemented to do any way-cool things that they want to do without an > update to firmware, right? ...and current versions of the kernel can > just shed permissions if they don't want them. > > ...so if I understand correctly, "Secure SVC" mode is more permissive > than "Non Secure HYP" mode, right? It looks to me as if we currently > start the kernel in "Secure SVC" mode. What do you think about the > kernel detecting Secure SVC and then dropping down permission levels > (to Non Secure HYP). Once it did this, it could update things like > the virtual offset and then transition down further into non-secure > SVC mode. > > ...or maybe this has been discussed millions of times already and I'm > just clueless. ...or maybe this is just too hard for the kernel to do > in a generic way? I think this is a great idea. When running on simulators, it would make (the non-DTB parts of) the bootwrapper and QEMU's built-in bootloader unnecessary. Implementing it on AArch64 should be trivial as you can just read CurrentEL and work from whatever EL/PL you're at. Is there an easy way to check whether you're in secure or nonsecure mode in AArch32? I seem to recall discussion about putting this information into the DTB, which makes me think there isn't. Christopher -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation.