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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3ED6C28D13 for ; Thu, 25 Aug 2022 15:25:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242697AbiHYPZz (ORCPT ); Thu, 25 Aug 2022 11:25:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36856 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242466AbiHYPZH (ORCPT ); Thu, 25 Aug 2022 11:25:07 -0400 Received: from out30-42.freemail.mail.aliyun.com (out30-42.freemail.mail.aliyun.com [115.124.30.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C034E52DF7 for ; Thu, 25 Aug 2022 08:25:04 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046059;MF=liusong@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0VNE9SFS_1661441100; Received: from 30.15.198.241(mailfrom:liusong@linux.alibaba.com fp:SMTPD_---0VNE9SFS_1661441100) by smtp.aliyun-inc.com; Thu, 25 Aug 2022 23:25:01 +0800 Message-ID: <6d6a7c14-ab8f-ef6f-8e9b-54732abaf3e3@linux.alibaba.com> Date: Thu, 25 Aug 2022 23:25:00 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.0.3 Subject: Re: [PATCH] arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually From: Liu Song To: catalin.marinas@arm.com, will@kernel.org, james.morse@arm.com Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <1659691274-48554-1-git-send-email-liusong@linux.alibaba.com> In-Reply-To: <1659691274-48554-1-git-send-email-liusong@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Is there any potential problem with this modification? Looking forward to your reply. Thanks > From: Liu Song > > In our environment, it was found that the mitigation BHB has a great > impact on the benchmark performance. For example, in the lmbench test, > the "process fork && exit" test performance drops by 20%. > So it is necessary to have the ability to turn off the mitigation > individually through cmdline, thus avoiding having to compile the > kernel by adjusting the config. > > Signed-off-by: Liu Song > --- > arch/arm64/kernel/proton-pack.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c > index 40be3a7..bd16903 100644 > --- a/arch/arm64/kernel/proton-pack.c > +++ b/arch/arm64/kernel/proton-pack.c > @@ -988,6 +988,14 @@ static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot) > isb(); > } > > +static bool __read_mostly __nospectre_bhb; > +static int __init parse_spectre_bhb_param(char *str) > +{ > + __nospectre_bhb = true; > + return 0; > +} > +early_param("nospectre_bhb", parse_spectre_bhb_param); > + > void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry) > { > bp_hardening_cb_t cpu_cb; > @@ -1001,7 +1009,7 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry) > /* No point mitigating Spectre-BHB alone. */ > } else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) { > pr_info_once("spectre-bhb mitigation disabled by compile time option\n"); > - } else if (cpu_mitigations_off()) { > + } else if (cpu_mitigations_off() || __nospectre_bhb) { > pr_info_once("spectre-bhb mitigation disabled by command line option\n"); > } else if (supports_ecbhb(SCOPE_LOCAL_CPU)) { > state = SPECTRE_MITIGATED;