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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY 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 8A750C43331 for ; Tue, 31 Mar 2020 23:35:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 54F0220772 for ; Tue, 31 Mar 2020 23:35:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731527AbgCaXfV (ORCPT ); Tue, 31 Mar 2020 19:35:21 -0400 Received: from eddie.linux-mips.org ([148.251.95.138]:54170 "EHLO cvs.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731259AbgCaXfV (ORCPT ); Tue, 31 Mar 2020 19:35:21 -0400 Received: (from localhost user: 'macro', uid#1010) by eddie.linux-mips.org with ESMTP id S23991035AbgCaXfQ0q2BF (ORCPT ); Wed, 1 Apr 2020 01:35:16 +0200 Date: Wed, 1 Apr 2020 00:35:16 +0100 (BST) From: "Maciej W. Rozycki" To: Thomas Gleixner cc: hpa@zytor.com, Andrew Cooper , LKML , Ingo Molnar , Borislav Petkov , x86@kernel.org, Jan Kiszka , James Morris , David Howells , Matthew Garrett , Josh Boyer , Zhenzhong Duan , Steve Wahl , Mike Travis , Dimitri Sivanich , Arnd Bergmann , "Peter Zijlstra (Intel)" , Giovanni Gherdovich , "Rafael J. Wysocki" , Len Brown , Kees Cook , Martin Molnar , Pingfan Liu , jailhouse-dev@googlegroups.com Subject: Re: [PATCH] x86/smpboot: Remove 486-isms from the modern AP boot path In-Reply-To: <87r1xgxzy6.fsf@nanos.tec.linutronix.de> Message-ID: References: <20200325101431.12341-1-andrew.cooper3@citrix.com> <601E644A-B046-4030-B3BD-280ABF15BF53@zytor.com> <87r1xgxzy6.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 25 Mar 2020, Thomas Gleixner wrote: > >>@@ -1118,7 +1121,7 @@ static int do_boot_cpu(int apicid, int cpu, > >>struct task_struct *idle, > >> } > >> } > >> > >>- if (x86_platform.legacy.warm_reset) { > >>+ if (!APIC_INTEGRATED(boot_cpu_apic_version)) { > >> /* > >> * Cleanup possible dangling ends... > >> */ > > > > We don't support SMP on 486 and haven't for a very long time. Is there > > any reason to retain that code at all? > > Not that I'm aware off. For the record: this code is for Pentium really, covering original P5 systems, which lacked integrated APIC, as well as P54C systems that went beyond dual (e.g. ALR made quad-SMP P54C systems). They all used external i82489DX APICs for SMP support. Few were ever manufactured and getting across one let alone running Linux might be tough these days. I never managed to get one for myself, which would have been helpful for maintaining this code. Even though we supported them by spec I believe we never actually ran MP on any 486 SMP system (Alan Cox might be able to straighten me out on this); none that I know of implemented the MPS even though actual hardware might have used the APIC architecture. Compaq had its competing solution for 486 and newer SMP, actually deployed, the name of which I long forgot. We never supported it due to the lack of documentation combined with the lack of enough incentive for someone to reverse-engineer it. FWIW, Maciej