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_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 B7A72ECDE46 for ; Sun, 28 Oct 2018 09:44:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5E31120664 for ; Sun, 28 Oct 2018 09:44:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5E31120664 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 S1727338AbeJ1SRT (ORCPT ); Sun, 28 Oct 2018 14:17:19 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:50617 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726195AbeJ1SRT (ORCPT ); Sun, 28 Oct 2018 14:17:19 -0400 Received: from p5492fe24.dip0.t-ipconnect.de ([84.146.254.36] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1gGhR7-0005VW-EZ; Sun, 28 Oct 2018 10:32:46 +0100 Date: Sun, 28 Oct 2018 10:32:38 +0100 (CET) From: Thomas Gleixner To: Tim Chen cc: Waiman Long , 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 , linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [Patch v3 03/13] x86/speculation: Add static key for Enhanced IBRS In-Reply-To: <90d6723f-9cb9-e299-3e99-fa01c2518c29@linux.intel.com> Message-ID: References: <90d6723f-9cb9-e299-3e99-fa01c2518c29@linux.intel.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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 On Fri, 26 Oct 2018, Tim Chen wrote: > On 10/26/2018 09:58 AM, Waiman Long wrote: > >> @@ -386,6 +389,7 @@ static void __init spectre_v2_select_mitigation(void) > >> /* Force it so VMEXIT will restore correctly */ > >> x86_spec_ctrl_base |= SPEC_CTRL_IBRS; > >> wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); > >> + static_branch_enable(&spectre_v2_enhanced_ibrs); > >> goto specv2_set_mode; > >> } > >> if (IS_ENABLED(CONFIG_RETPOLINE)) > > > > Why you need a static key for enhanced IBRS? It is supposed to be set at > > boot time and never get changed after that. It will be easier to use a > > feature bit for that instead. We usually use static key when the value > > can be changed at run time. > > > > We're close to running out of the feature bits. So I'm trying not to > use those. Software feature bits can be extended when needed. That's really a non issue. Thanks, tglx