Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752928AbeADSxF (ORCPT + 1 other); Thu, 4 Jan 2018 13:53:05 -0500 Received: from www.llwyncelyn.cymru ([82.70.14.225]:46662 "EHLO fuzix.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752780AbeADSxC (ORCPT ); Thu, 4 Jan 2018 13:53:02 -0500 Date: Thu, 4 Jan 2018 18:50:43 +0000 From: Alan Cox To: Tim Chen Cc: Thomas Gleixner , Andy Lutomirski , Linus Torvalds , Greg KH , Dave Hansen , Andrea Arcangeli , Andi Kleen , Arjan Van De Ven , linux-kernel@vger.kernel.org Subject: Re: [PATCH 6/7] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC_CTRL feature Message-ID: <20180104185043.16e9390d@alans-desktop> In-Reply-To: <4d4b3752e8e533201c6983d8473eea95c747ea33.1515086770.git.tim.c.chen@linux.intel.com> References: <4d4b3752e8e533201c6983d8473eea95c747ea33.1515086770.git.tim.c.chen@linux.intel.com> Organization: Intel Corporation X-Mailer: Claws Mail 3.15.1-dirty (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Thu, 4 Jan 2018 09:56:47 -0800 Tim Chen wrote: > There are 2 ways to control IBRS > > 1. At boot time > noibrs kernel boot parameter will disable IBRS usage > > Otherwise if the above parameters are not specified, the system > will enable ibrs and ibpb usage if the cpu supports it. > > 2. At run time > echo 0 > /sys/kernel/debug/ibrs_enabled will turn off IBRS > echo 1 > /sys/kernel/debug/ibrs_enabled will turn on IBRS in kernel > echo 2 > /sys/kernel/debug/ibrs_enabled will turn on IBRS in both userspace and kernel > > The implementation was updated with input from Andrea Arcangeli. > Why are these under debug ? This isn't a debugging thing. Alan