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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 3C63AC43441 for ; Mon, 19 Nov 2018 12:58:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0DD20208E4 for ; Mon, 19 Nov 2018 12:58:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0DD20208E4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728997AbeKSXWD (ORCPT ); Mon, 19 Nov 2018 18:22:03 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:38377 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728967AbeKSXWD (ORCPT ); Mon, 19 Nov 2018 18:22:03 -0500 Received: from hsi-kbw-5-158-153-52.hsi19.kabel-badenwuerttemberg.de ([5.158.153.52] 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 1gOj83-0006su-Jw; Mon, 19 Nov 2018 13:58:15 +0100 Date: Mon, 19 Nov 2018 13:58:15 +0100 (CET) From: Thomas Gleixner To: Tim Chen cc: Jiri Kosina , Tom Lendacky , Ingo Molnar , Peter Zijlstra , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Andi Kleen , Dave Hansen , Casey Schaufler , Asit Mallick , Arjan van de Ven , Jon Masters , Waiman Long , linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [Patch v5 08/16] smt: Create cpu_smt_enabled static key for SMT specific code In-Reply-To: <91b719e53640f60666b40a3516da2b80703b2f76.1542418937.git.tim.c.chen@linux.intel.com> Message-ID: References: <91b719e53640f60666b40a3516da2b80703b2f76.1542418937.git.tim.c.chen@linux.intel.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) 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 Fri, 16 Nov 2018, Tim Chen wrote: > In later code, STIBP will be turned on/off in the context switch code > path when SMT is enabled. Checks for SMT is best > avoided on such hot paths. > > Create cpu_smt_enabled static key to turn on such SMT specific code > statically. > > This key is set in code under hot plug, so it is limited in > scope to architecture supporting CPU hotplug, like x86. The key is enabled by default and its scope has nothing to do with CPU hotplug. It depends on CONFIG_HOTPLUG_SMT which is the extra SMT control code which is currently only enabled on x86. > diff --git a/include/linux/cpu.h b/include/linux/cpu.h > index 218df7f..b54f085 100644 > --- a/include/linux/cpu.h > +++ b/include/linux/cpu.h > @@ -188,5 +188,6 @@ static inline void cpu_smt_disable(bool force) { } > static inline void cpu_smt_check_topology_early(void) { } > static inline void cpu_smt_check_topology(void) { } > #endif > +DECLARE_STATIC_KEY_TRUE(cpu_smt_enabled); And here it is declared unconditionally which allows code to use it despite CONFIG_HOTPLUG_SMT=n and subsequently breaks the build. Thanks, tglx