From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1948919AbcBSBIG (ORCPT ); Thu, 18 Feb 2016 20:08:06 -0500 Received: from mail-wm0-f44.google.com ([74.125.82.44]:33115 "EHLO mail-wm0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1947650AbcBSBID (ORCPT ); Thu, 18 Feb 2016 20:08:03 -0500 Message-ID: <1455844078.31619.297.camel@nexus-software.ie> Subject: Re: [PATCH] x86/intel/quark: Parameterize the kernel's IMR lock logic From: "Bryan O'Donoghue" To: Ingo Molnar 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 Date: Fri, 19 Feb 2016 01:07:58 +0000 In-Reply-To: <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> <20160218185322.GC16753@gmail.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5-1ubuntu3.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2016-02-18 at 19:53 +0100, Ingo Molnar wrote: > * 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. I'm in favour of that too. Charitably I think locking a register like this makes sense only when you talk about it in a meeting room somewhere; as soon as you go to try to use it in a real situation you find its far more trouble than its really worth. So, I'm going to trim that out of this code unless I hear some pushback from elsewhere in the 1/2 day or so. > > Yeah, it's a nice looking hardware feature - but I don't think it's > particularly > useful in terms of extra protection. > > Thanks, > > Ingo