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 9D33EEB64DC for ; Thu, 22 Jun 2023 02:14:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230163AbjFVCOE (ORCPT ); Wed, 21 Jun 2023 22:14:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39896 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229535AbjFVCOC (ORCPT ); Wed, 21 Jun 2023 22:14:02 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B1D5C1731 for ; Wed, 21 Jun 2023 19:13:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1687399989; 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=ZrXJwF8ZKTlwhPXSIVwgN09FFhnrhvULSTkbHyhZp9M=; b=b3XsClECy+XdExwpLyDsj3M0wFlJrTp3u5/cu4jpYRhbm3WTq1raQbHRTgh4LEXg9DTRfF aFGAV39EYWh5i/nk/XlOpI0YvxsYg38I8WlNRO4BcsgLkV9NBCkwszf1rlF84AZ1byCd8P cwZ7kIYAbJQVvxVs1mPzrs1uoHlixdw= 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-662-B7PoQ7nGNbesStlMwdqg3A-1; Wed, 21 Jun 2023 22:13:06 -0400 X-MC-Unique: B7PoQ7nGNbesStlMwdqg3A-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 498C788CC42; Thu, 22 Jun 2023 02:13:05 +0000 (UTC) Received: from [10.22.33.143] (unknown [10.22.33.143]) by smtp.corp.redhat.com (Postfix) with ESMTP id 404FD200BA8B; Thu, 22 Jun 2023 02:13:04 +0000 (UTC) Message-ID: <8df8ea62-11af-fdac-9561-a6bd6a41e83a@redhat.com> Date: Wed, 21 Jun 2023 22:13:04 -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 v3 1/3] x86/idle: Disable IBRS when cpu is offline Content-Language: en-US To: Randy Dunlap , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Josh Poimboeuf , Pawan Gupta , Jacob Pan , Len Brown Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-pm@vger.kernel.org, Robin Jarry , Joe Mario References: <20230622003603.1188364-1-longman@redhat.com> <20230622003603.1188364-2-longman@redhat.com> <8a1ba9cd-426f-dd59-bb2a-67a0f1af6de8@infradead.org> From: Waiman Long In-Reply-To: <8a1ba9cd-426f-dd59-bb2a-67a0f1af6de8@infradead.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/21/23 22:05, Randy Dunlap wrote: > > On 6/21/23 17:36, 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. When the CPU is online again, it will be re-initialized >> and so restoring the SPEC_CTRL value isn't needed. >> >> Add a comment to say that native_play_dead() is a __noreturn function, >> but it can't be marked as such to avoid confusion about the missing >> MSR restoration code. >> >> Signed-off-by: Waiman Long >> --- >> arch/x86/kernel/smpboot.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c >> index 352f0ce1ece4..7bc33885518c 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); >> @@ -1836,8 +1837,17 @@ void __noreturn hlt_play_dead(void) >> } >> } >> >> +/* >> + * naitve_play_dead() is essentially a __noreturn function, but it can't > typo: native_play_dead() Thanks for spotting the typo. Will fix it in the next version. Cheers, Longman > >> + * be marked as such as the compiler may complain about it. >> + */ >> void native_play_dead(void) >> { >> + 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); >>