From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752757AbeB1N0n (ORCPT ); Wed, 28 Feb 2018 08:26:43 -0500 Received: from mga01.intel.com ([192.55.52.88]:23688 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752565AbeB1N0l (ORCPT ); Wed, 28 Feb 2018 08:26:41 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.47,405,1515484800"; d="scan'208";a="21428012" Date: Wed, 28 Feb 2018 05:26:40 -0800 From: "Raj, Ashok" To: Henrique de Moraes Holschuh Cc: Borislav Petkov , X86 ML , Arjan Van De Ven , Tom Lendacky , LKML , Ashok Raj Subject: Re: [PATCH 4/7] x86/microcode: Do not upload microcode if CPUs are offline Message-ID: <20180228132639.GA23235@araj-mobl1.jf.intel.com> References: <20180228102846.13447-1-bp@alien8.de> <20180228102846.13447-5-bp@alien8.de> <20180228131156.i4y6la7besdflffd@khazad-dum.debian.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180228131156.i4y6la7besdflffd@khazad-dum.debian.net> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 28, 2018 at 10:11:56AM -0300, Henrique de Moraes Holschuh wrote: > > Avoid loading microcode if any of the CPUs are offline, and issue a > > warning. Having different microcode revisions on the system at any time > > is outright dangerous. > > Even if we update that microcode during CPU early bring-up, before we > mark it on-line and start using it? > > AFAIK, late-loading or not, this is what should happen in the current > code: APs that are brought up after a microcode update is loaded (either > by the early or late driver, it doesn't matter) will be always > *early-updated* to the new microcode. > > Is it dangerous to have an offline core at an older microcode revision > than the online cores? We don't want to leave a system and allow the user to update microcode when some cpus are offline. Remember cpu_offline in linux is only logical offlining.. so the cpu is still in the system.. it can even participate in MCE for e.g. It is very much alive. Its not a question that "Would it not work" but its not worth to leave an open door and being paranoid is best! > > I am not against the patch, mind you, but I am curious about why it is > supposed to be dangerous if we're updating the CPUs before we start > using them *anyway*. > > Also, if this is really dangerous, does it means safe CPU hotplug isn't > possible? AFAICT, the firmware would have to do it for us, but it > *doesn't* have the up-to-date microcode (*we* had to update it)... The difference is hot-adding you know you are going to update the current microcode. But leaving a cpu in offline state is leaving it stale for a long time without realizing that you have some stale cores.