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 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 DF521C55199 for ; Sun, 26 Apr 2020 10:39:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B70762070A for ; Sun, 26 Apr 2020 10:39:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726154AbgDZKji (ORCPT ); Sun, 26 Apr 2020 06:39:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726116AbgDZKjh (ORCPT ); Sun, 26 Apr 2020 06:39:37 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8507AC061A0C for ; Sun, 26 Apr 2020 03:39:37 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jSehB-0002IN-2p; Sun, 26 Apr 2020 12:39:33 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 81251100605; Sun, 26 Apr 2020 12:39:32 +0200 (CEST) From: Thomas Gleixner To: Holger Schurig Cc: "linux-kernel\@vger.kernel.org" , x86@kernel.org, Arnd Bergmann Subject: Re: BUG 5.5.6, from patch "cpu/SMT: Fix x86 link error without CONFIG_SYSFS" In-Reply-To: References: Date: Sun, 26 Apr 2020 12:39:32 +0200 Message-ID: <875zdmttsr.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Holger, Holger Schurig writes: > if one compiled kernel 5.6.6 with CONFIG_HOTPLUG_CPU=n, then the > compilation will fail. The reason is your patch, which introduces > this: > +int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval) It would have been more helpful to provide the actual commit SHA instead of copying tons of patch code. > It happens that cpu_down_maps_locked is only defined when > CONFIG_HOTPLUG_CPU=y, but not otherwise. Right. > On my embedded target I so far had the CPU hotplugging off. After all, > the CPU is physically soldered, there will never be a hotplugging > happen. CPU hotplug is used for far more than physical hotplug. SMT control depends on it in order to apply speculation mitigations, hibernation requires working CPU hotplug as well. As the speculation mess requires SMT control we more or less have to make CPU hotplug mandatory on x86... Thanks, tglx