From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752076AbaHaTs4 (ORCPT ); Sun, 31 Aug 2014 15:48:56 -0400 Received: from terminus.zytor.com ([198.137.202.10]:42356 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751235AbaHaTsw (ORCPT ); Sun, 31 Aug 2014 15:48:52 -0400 Message-ID: <54037C07.8060703@zytor.com> Date: Sun, 31 Aug 2014 12:48:23 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0 MIME-Version: 1.0 To: Henrique de Moraes Holschuh , Borislav Petkov , Fenghua Yu CC: linux-kernel@vger.kernel.org Subject: Re: early microcode: how to disable at runtime? References: <20140809231911.GA4843@khazad-dum.debian.net> <20140831194548.GA12628@khazad-dum.debian.net> In-Reply-To: <20140831194548.GA12628@khazad-dum.debian.net> 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 08/31/2014 12:45 PM, Henrique de Moraes Holschuh wrote: > Currently, there is no way to disable early microcode update at runtime. If > an early initramfs with microcode update data is available, it will always > be used. > > This can be a very big deal when things go wrong: it is hard for the regular > user to recover from an initramfs image that crashes the system, and the > early initramfs has no "disable" trigger. > > In the general case, booting from rescue media will be required to fix the > system. > > Unfortunately, the BSP microcode update is handled before early_param() is > available, so a kernel command line parameter to disable early microcode > updates for the BSP isn't easily possible. > > Other than duplicating much of the code in parse_early_param/parse_args to > search for a "noearlymcu" parameter, is there any other way we could add a > disable switch for the early microcode update system? > Probably more like something more like arch/x86/boot/cmdline.c. Maybe we could even make it sharable. -hpa