From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752747AbeB1NMD (ORCPT ); Wed, 28 Feb 2018 08:12:03 -0500 Received: from out5-smtp.messagingengine.com ([66.111.4.29]:40195 "EHLO out5-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752329AbeB1NMA (ORCPT ); Wed, 28 Feb 2018 08:12:00 -0500 X-ME-Sender: Date: Wed, 28 Feb 2018 10:11:56 -0300 From: Henrique de Moraes Holschuh To: Borislav Petkov Cc: X86 ML , Arjan Van De Ven , Ashok Raj , Tom Lendacky , LKML Subject: Re: [PATCH 4/7] x86/microcode: Do not upload microcode if CPUs are offline Message-ID: <20180228131156.i4y6la7besdflffd@khazad-dum.debian.net> References: <20180228102846.13447-1-bp@alien8.de> <20180228102846.13447-5-bp@alien8.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180228102846.13447-5-bp@alien8.de> X-GPG-Fingerprint1: 4096R/0x0BD9E81139CB4807: C467 A717 507B BAFE D3C1 6092 0BD9 E811 39CB 4807 User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 28 Feb 2018, Borislav Petkov 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? 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)... -- Henrique Holschuh