From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754837AbcAHMSY (ORCPT ); Fri, 8 Jan 2016 07:18:24 -0500 Received: from unicorn.mansr.com ([81.2.72.234]:43089 "EHLO unicorn.mansr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754520AbcAHMSX convert rfc822-to-8bit (ORCPT ); Fri, 8 Jan 2016 07:18:23 -0500 From: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= To: Borislav Petkov Cc: Thomas Voegtle , Markus Trippelsdorf , linux-kernel@vger.kernel.org Subject: Re: x86/microcode update on systems without INITRD References: <20151119225828.GB4926@pd.tnic> <20151120071920.GA321@x4> <20151120082716.GA4028@pd.tnic> <20160107121841.GB16472@pd.tnic> <20160108105900.GA14673@pd.tnic> <20160108113641.GE14673@pd.tnic> <20160108120812.GF14673@pd.tnic> Date: Fri, 08 Jan 2016 12:18:15 +0000 In-Reply-To: <20160108120812.GF14673@pd.tnic> (Borislav Petkov's message of "Fri, 8 Jan 2016 13:08:12 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Borislav Petkov writes: > On Fri, Jan 08, 2016 at 11:46:28AM +0000, Måns Rullgård wrote: >> How is an initrd different from a real filesystem as seen by the >> microcode update driver? > > For starters, initrd is available much earlier, even before paging is > enabled on 32-bit, for example. See find_cpio_data(). Yes, but the microcode driver doesn't care about this AFAICT. >> The objection against removing the dependency was that updating >> microcode "late" isn't safe. I don't see how turning on BLK_DEV_INITRD >> stops anyone doing those allegedly unsafe updates anyway. > > No one is stopping anyone from doing late updates. It is a valid use > case, and we have to support it. And late updates are not necessarily > unsafe, per se. So it's meant to be supported, good. > Lemme put it this way: it is a lot less unproblematic to do early > updates. Mind you, there's no 100% guarantee that early updates would > always work either. It all depends on what the microcode patch does. But > they do work 99,9999999...% of the time. :) > > IOW, I haven't heard of an early update breaking the machine. But it is > possible. > > So the *general* flow should be that people enable BLK_DEV_INITRD, > put the microcode in there and it gets updated as early as possible. > This is what the distros do and it is the most tested path. The other > possibilities are there too, but only for cases where initrd is out of > the question. Yes, that's the common case, and those users will have BLK_DEV_INITRD enabled anyway. Now why should someone who, for whatever reasons, is doing microcode updates late be forced to enable BLK_DEV_INITRD even though he doesn't use it? -- Måns Rullgård