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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT 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 DACC1C43381 for ; Thu, 28 Feb 2019 18:21:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BD663218CD for ; Thu, 28 Feb 2019 18:21:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732656AbfB1SVd (ORCPT ); Thu, 28 Feb 2019 13:21:33 -0500 Received: from foss.arm.com ([217.140.101.70]:52454 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726203AbfB1SVc (ORCPT ); Thu, 28 Feb 2019 13:21:32 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id ED7D5EBD; Thu, 28 Feb 2019 10:21:31 -0800 (PST) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9329F3F5C1; Thu, 28 Feb 2019 10:21:29 -0800 (PST) Date: Thu, 28 Feb 2019 18:21:27 +0000 From: Catalin Marinas To: Suzuki K Poulose Cc: jeremy.linton@arm.com, linux-arm-kernel@lists.infradead.org, will.deacon@arm.com, marc.zyngier@arm.com, dave.martin@arm.com, shankerd@codeaurora.org, julien.thierry@arm.com, mlangsdo@redhat.com, stefan.wahren@i2e.com, andre.przywara@arm.com, linux-kernel@vger.kernel.org, corbet@lwn.net, linux-doc@vger.kernel.org Subject: Re: [PATCH v5 01/10] arm64: Provide a command line to disable spectre_v2 mitigation Message-ID: <20190228182126.GA252518@arrakis.emea.arm.com> References: <20190227010544.597579-1-jeremy.linton@arm.com> <20190227010544.597579-2-jeremy.linton@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 28, 2019 at 06:14:34PM +0000, Suzuki K Poulose wrote: > On 27/02/2019 01:05, Jeremy Linton wrote: > > There are various reasons, including bencmarking, to disable spectrev2 > > mitigation on a machine. Provide a command-line to do so. > > > > Signed-off-by: Jeremy Linton > > Cc: Jonathan Corbet > > Cc: linux-doc@vger.kernel.org > > > > diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c > > index 9950bb0cbd52..d2b2c69d31bb 100644 > > --- a/arch/arm64/kernel/cpu_errata.c > > +++ b/arch/arm64/kernel/cpu_errata.c > > @@ -220,6 +220,14 @@ static void qcom_link_stack_sanitization(void) > > : "=&r" (tmp)); > > } > > +static bool __nospectre_v2; > > +static int __init parse_nospectre_v2(char *str) > > +{ > > + __nospectre_v2 = true; > > + return 0; > > +} > > +early_param("nospectre_v2", parse_nospectre_v2); > > + > > static void > > enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry) > > { > > @@ -231,6 +239,11 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry) > > if (!entry->matches(entry, SCOPE_LOCAL_CPU)) > > return; > > + if (__nospectre_v2) { > > + pr_info_once("spectrev2 mitigation disabled by command line option\n"); > > + return; > > + } > > + > > Could we not disable the "cap" altogether instead, rather than disabling the > work around ? Or do we need that information ? There are a few ideas here but I think we settled on always reporting in sysfs even if the mitigation is disabled in .config. So I guess we need the "cap" around for the reporting part. -- Catalin