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, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 D07EAC43441 for ; Wed, 21 Nov 2018 20:36:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A27E2214E0 for ; Wed, 21 Nov 2018 20:36:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A27E2214E0 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 S2389643AbeKVHMr (ORCPT ); Thu, 22 Nov 2018 02:12:47 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:45600 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730044AbeKVHMr (ORCPT ); Thu, 22 Nov 2018 02:12:47 -0500 Received: from p4fea46ac.dip0.t-ipconnect.de ([79.234.70.172] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1gPZEu-0000oe-2Q; Wed, 21 Nov 2018 21:36:48 +0100 Date: Wed, 21 Nov 2018 21:36:47 +0100 (CET) From: Thomas Gleixner To: Borislav Petkov cc: LKML , x86@kernel.org, Peter Zijlstra , Andy Lutomirski , Linus Torvalds , Jiri Kosina , Tom Lendacky , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Andi Kleen , Dave Hansen , Casey Schaufler , Asit Mallick , Arjan van de Ven , Jon Masters , Waiman Long , Greg KH , Dave Stewart , Kees Cook , Tim Chen Subject: Re: [patch 05/24] x86/speculation: Disable STIBP when enhanced IBRS is in use In-Reply-To: <20181121203353.GD27559@zn.tnic> Message-ID: References: <20181121201430.559770965@linutronix.de> <20181121201722.717439984@linutronix.de> <20181121203353.GD27559@zn.tnic> 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 Wed, 21 Nov 2018, Borislav Petkov wrote: > On Wed, Nov 21, 2018 at 09:14:35PM +0100, Thomas Gleixner wrote: > > From: Tim Chen > > > > If enhanced IBRS is active, STIBP is redundant for mitigating Spectre v2 > > user space exploits from hyperthread sibling. > > > > Disable STIBP when enhanced IBRS is used. > > > > Signed-off-by: Tim Chen > > Signed-off-by: Thomas Gleixner > > > > --- > > arch/x86/kernel/cpu/bugs.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > --- a/arch/x86/kernel/cpu/bugs.c > > +++ b/arch/x86/kernel/cpu/bugs.c > > @@ -321,6 +321,10 @@ static bool stibp_needed(void) > > if (spectre_v2_enabled == SPECTRE_V2_NONE) > > return false; > > > > + /* Enhanced IBRS makes using STIBP unnecessary. */ > > + if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED) > > + return false; > > + > > if (!boot_cpu_has(X86_FEATURE_STIBP)) > > return false; > > > > @@ -846,6 +850,9 @@ static ssize_t l1tf_show_state(char *buf > > > > static char *stibp_state(void) > > { > > + if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED) > > + return ""; > > If > spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED > > then SPEC_CTRL_STIBP should not be set in x86_spec_ctrl_base > (stibp_needed() prevents the setting in arch_smt_update()) so the above > check should not be needed. > > I *think*. Yes, makes sense. Thanks, tglx