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 4F3E9EB64D8 for ; Wed, 21 Jun 2023 14:45:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231338AbjFUOpw (ORCPT ); Wed, 21 Jun 2023 10:45:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53824 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232245AbjFUOpO (ORCPT ); Wed, 21 Jun 2023 10:45:14 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE04CBC for ; Wed, 21 Jun 2023 07:44:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1687358671; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4VfIt4Fzbnh6aUb6TyZcqNjXNhG3BKZH5u5zEbS39GE=; b=K1yk+X3oZAb1BnM9k17T0dWgRCJSdE2WfA1OlWT3rGweGXvYp6hVNfHlP9qR00LJaKg0Gh 9c656KnqfS4DQFgcjZpBme4k22xVE/ehVGA487BXuTCQh/ppXfBoKqKJ5cKABbmnmiY9xN g6ucz0rEx9AxXyObjJ4z3tdxTWaXXHI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-553-9_xWp-wSOkus_YXxvzQhoQ-1; Wed, 21 Jun 2023 10:44:25 -0400 X-MC-Unique: 9_xWp-wSOkus_YXxvzQhoQ-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2749D89224F; Wed, 21 Jun 2023 14:44:24 +0000 (UTC) Received: from [10.22.17.140] (unknown [10.22.17.140]) by smtp.corp.redhat.com (Postfix) with ESMTP id 704D6492B01; Wed, 21 Jun 2023 14:44:23 +0000 (UTC) Message-ID: <5cb81f3b-45a0-d566-3d63-569b5706e9fe@redhat.com> Date: Wed, 21 Jun 2023 10:44:23 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH v2 2/5] x86/idle: Disable IBRS when cpu is offline Content-Language: en-US To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Josh Poimboeuf , Pawan Gupta , Jacob Pan , Len Brown , linux-kernel@vger.kernel.org, x86@kernel.org, linux-pm@vger.kernel.org, Robin Jarry , Joe Mario References: <20230620140625.1001886-1-longman@redhat.com> <20230620140625.1001886-3-longman@redhat.com> <20230621072313.GA2046280@hirez.programming.kicks-ass.net> <7f2424df-1846-6c38-e446-b3d5aa693ecd@redhat.com> <20230621143602.GI2053369@hirez.programming.kicks-ass.net> From: Waiman Long In-Reply-To: <20230621143602.GI2053369@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/21/23 10:36, Peter Zijlstra wrote: > On Wed, Jun 21, 2023 at 09:59:52AM -0400, Waiman Long wrote: >> On 6/21/23 03:23, Peter Zijlstra wrote: >>> On Tue, Jun 20, 2023 at 10:06:22AM -0400, Waiman Long wrote: >>>> Commit bf5835bcdb96 ("intel_idle: Disable IBRS during long idle") >>>> disables IBRS when the CPU enters long idle. However, when a CPU becomes >>>> offline, the IBRS bit is still set when X86_FEATURE_KERNEL_IBRS is >>>> enabled. That will impact the performance of a sibling CPU. Mitigate >>>> this performance impact by clearing all the mitigation bits in SPEC_CTRL >>>> MSR when offline and restoring the value of the MSR when it becomes >>>> online again. >>>> >>>> Signed-off-by: Waiman Long >>>> --- >>>> arch/x86/kernel/smpboot.c | 13 +++++++++++++ >>>> 1 file changed, 13 insertions(+) >>>> >>>> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c >>>> index 352f0ce1ece4..5ff82fef413c 100644 >>>> --- a/arch/x86/kernel/smpboot.c >>>> +++ b/arch/x86/kernel/smpboot.c >>>> @@ -84,6 +84,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> /* representing HT siblings of each logical CPU */ >>>> DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map); >>>> @@ -1838,12 +1839,24 @@ void __noreturn hlt_play_dead(void) >>>> void native_play_dead(void) >>>> { >>>> + u64 spec_ctrl = spec_ctrl_current(); >>>> + >>>> + if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS)) { >>>> + this_cpu_write(x86_spec_ctrl_current, 0); >>>> + native_wrmsrl(MSR_IA32_SPEC_CTRL, 0); >>>> + } >>>> + >>>> play_dead_common(); >>>> tboot_shutdown(TB_SHUTDOWN_WFS); >>>> mwait_play_dead(); >>>> if (cpuidle_play_dead()) >>>> hlt_play_dead(); >>>> + >>>> + if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS)) { >>>> + native_wrmsrl(MSR_IA32_SPEC_CTRL, spec_ctrl); >>>> + this_cpu_write(x86_spec_ctrl_current, spec_ctrl); >>>> + } >>>> } >>> play_dead() is marked __noreturn >> There are different versions of play_dead() in the kernel. Some of them are >> indeed marked __noreturn like the non-SMP one in arch/x86/kernel/process.c. >> The native_play_dead() that I am patching isn't one of those. > mostly by accident I think, hlt_play_dead() is, so I'm thinking > everybody (all compiler and objtool) managed to figure out > native_play_dead() is __noreturn too. Well, hlt_play_dead() is only called if cpuidle_play_dead() returns an error which is not the typical case. My testing does confirm that this patch is able to keep the IBRS bit off when a CPU is offline via its online sysfs file. Cheers, Longman