From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB35DC43331 for ; Sat, 7 Sep 2019 00:44:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C313D2173B for ; Sat, 7 Sep 2019 00:44:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393418AbfIGAdl (ORCPT ); Fri, 6 Sep 2019 20:33:41 -0400 Received: from mga12.intel.com ([192.55.52.136]:28273 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731527AbfIGAdk (ORCPT ); Fri, 6 Sep 2019 20:33:40 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Sep 2019 17:33:40 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,474,1559545200"; d="scan'208";a="213333308" Received: from araj-mobl1.jf.intel.com ([10.251.147.175]) by fmsmga002.fm.intel.com with ESMTP; 06 Sep 2019 17:33:39 -0700 Date: Fri, 6 Sep 2019 17:33:38 -0700 From: "Raj, Ashok" To: Thomas Gleixner Cc: Johannes Erdfelt , Borislav Petkov , Boris Ostrovsky , Mihai Carabas , "H. Peter Anvin" , Ingo Molnar , Jon Grimm , kanth.ghatraju@oracle.com, konrad.wilk@oracle.com, patrick.colp@oracle.com, Tom Lendacky , x86-ml , linux-kernel@vger.kernel.org, Ashok Raj Subject: Re: [PATCH] x86/microcode: Add an option to reload microcode even if revision is unchanged Message-ID: <20190907003338.GA14807@araj-mobl1.jf.intel.com> References: <41cee473-321c-2758-032a-ccf0f01359dc@oracle.com> <20190905002132.GA26568@otc-nc-03> <20190905072029.GB19246@zn.tnic> <20190905194044.GA3663@otc-nc-03> <20190905222706.GA4422@otc-nc-03> <20190906144039.GA29569@sventech.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 06, 2019 at 11:16:00PM +0200, Thomas Gleixner wrote: > > So if we want to do late microcode loading in a sane way then there are > only a few options and none of them exist today: > > 1) Micro-code contains a description of CPUID bits which are going to be > exposed after the load. Then the kernel can sanity check whether this > changes anything relevant or not. If there is a relevant change it can > reject the load and tell the admin that a reboot is required. This is pretty much what we had in mind when we suggested to the uCode teams. Just a process of providing a meta data file to accompany every uCode release. IMO new cpuid bits are probably less harmful than old ones dissappearing. > > 2) Rework CPUID feature handling so that it can reevaluate and reconfigure > the running system safely. There are a lot of things you need for that: > > A) Introduce a safe state for CPUs to reach which guarantees that none > of the CPUs will return from that state via a code path which > depends on previous state and might now go the other route with data > on the stack which only fits the previous configuration. > > B) Make all the cpufeature thingies run time switchable. That means > that you need to keep quite some code around which is currently init > only. That also means that you have to provide backout code for > things which set up data corresponding to cpu feature bits and so > forth. > > So #2 might be finished in about 20 years from now with the result that > some of the code pathes might simply still have a Maybe we can catch the kernel side in 20 years.. user space would still be busted, or have a fault way to control new cpuid much like how we do for VM's. > > if (cpufeature_changed()) > panic(); > > because there are things which you cannot back out. So the only sane > solution is to panic. Which is not a solution as it would be much more sane > to prevent late loading upfront and force people to reboot proper. > > Now #1 is actually a sensible and feasible solution which can be pulled off > in a reasonably short time frame, avoids all the bound to be ugly and > failure laden attempts of fixing late loading completely and provides a > usable and safe solution for joe user, jack admin and the super experts at > big-cloud corporate. > > That is not requiring any new format of microcode payload, as this can be > nicely done as a metadata package which comes with the microcode > payload. So you get the following backwards compatible states: > > Kernel metadata result > > old don't care refuse late load > > new No refuse late load > > new Yes decide based on metadata > > Thoughts? This is 100% in line with what we proposed... Cheers, Ashok