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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 6D093C43381 for ; Thu, 28 Feb 2019 18:25:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3E7D82070B for ; Thu, 28 Feb 2019 18:25:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732551AbfB1SZv (ORCPT ); Thu, 28 Feb 2019 13:25:51 -0500 Received: from foss.arm.com ([217.140.101.70]:52606 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726027AbfB1SZu (ORCPT ); Thu, 28 Feb 2019 13:25:50 -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 E93E7EBD; Thu, 28 Feb 2019 10:25:49 -0800 (PST) Received: from [10.1.196.93] (en101.cambridge.arm.com [10.1.196.93]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AE48E3F5C1; Thu, 28 Feb 2019 10:25:47 -0800 (PST) Subject: Re: [PATCH v5 01/10] arm64: Provide a command line to disable spectre_v2 mitigation To: catalin.marinas@arm.com 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 References: <20190227010544.597579-1-jeremy.linton@arm.com> <20190227010544.597579-2-jeremy.linton@arm.com> <20190228182126.GA252518@arrakis.emea.arm.com> From: Suzuki K Poulose Message-ID: <4ff13b4d-217e-38aa-c474-a0f357b1ccfb@arm.com> Date: Thu, 28 Feb 2019 18:25:46 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190228182126.GA252518@arrakis.emea.arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/02/2019 18:21, Catalin Marinas wrote: > 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. > Thanks Catalin. Reviewed-by: Suzuki K Poulose