From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1947368AbcBRSx2 (ORCPT ); Thu, 18 Feb 2016 13:53:28 -0500 Received: from mail-wm0-f54.google.com ([74.125.82.54]:37167 "EHLO mail-wm0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946716AbcBRSx0 (ORCPT ); Thu, 18 Feb 2016 13:53:26 -0500 Date: Thu, 18 Feb 2016 19:53:22 +0100 From: Ingo Molnar To: "Bryan O'Donoghue" Cc: linux-kernel@vger.kernel.org, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, andriy.shevchenko@linux.intel.com, boon.leong.ong@intel.com, fengguang.wu@intel.com, linux-doc@vger.kernel.org Subject: Re: [PATCH] x86/intel/quark: Parameterize the kernel's IMR lock logic Message-ID: <20160218185322.GC16753@gmail.com> References: <1455766168-17335-1-git-send-email-pure.logic@nexus-software.ie> <20160218075810.GA16041@gmail.com> <1455791503.31619.246.camel@nexus-software.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1455791503.31619.246.camel@nexus-software.ie> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Bryan O'Donoghue wrote: > On Thu, 2016-02-18 at 08:58 +0100, Ingo Molnar wrote: > > So why not simply do the patch below? Very few people use boot > > parameters, and the > > complexity does not seem to be worth it. > > > > Furthermore I think an IMR range in itself is safe enough - it's not > > like such > > register state is going to be randomly corrupted, even with the > > 'lock' bit unset. > > > Hi Ingo. > > I agree - to flip the lock bit you need to be in ring-0 anyway. > > > So it's a perfectly fine protective measure against accidental memory > > corruption > > from the DMA space. It should not try to be more than that. > > > > And once we do this, I suggest we get rid of the 'lock' parameter > > altogether - > > that will further simplify the code. > > > > Thanks, > > > > Ingo > > That was the V1 of this patch > > https://groups.google.com/forum/#!topic/linux.kernel/6ZuVOF3TJow heh ;-) > Andriy asked for the boot parameter to control the state of the IMR > lock bit, I'm just as happy to go back to that version TBH I really think it's over-engineered - especially considering that with the kernel lock-down removed there's no other IMR area that is really locked down - so we could get rid of the whole 'locked' logic that would simplify the code throughout. Yeah, it's a nice looking hardware feature - but I don't think it's particularly useful in terms of extra protection. Thanks, Ingo