From patchwork Mon Jul 10 19:48:54 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 13307544 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 48006EB64DC for ; Mon, 10 Jul 2023 19:50:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231319AbjGJTuA (ORCPT ); Mon, 10 Jul 2023 15:50:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51456 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230080AbjGJTt7 (ORCPT ); Mon, 10 Jul 2023 15:49:59 -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 DAE7D197 for ; Mon, 10 Jul 2023 12:49:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1689018553; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ynX4xs1ia0vVamnWxq7T+G8TSAYpJrKtW6apk2sxnag=; b=Vn1lcn6Kh5qxUrC2z/m43BkqCc/Xl8L4w9MRDHFa9WgEdki6PiLdWfU9Rx0LP7KQZGdM+k nmVGlcnAUYoSUSvvOeaBGn5j9FiZ/GYm0SjjDxJk1lp68VXQtN9fIsFAm7rSHfo6liS+/U b9xT1Ass0X2a0p+HK+rJG+5tAcsKC3g= 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-250-CSDJodKQPdmD9xBscMj83Q-1; Mon, 10 Jul 2023 15:49:09 -0400 X-MC-Unique: CSDJodKQPdmD9xBscMj83Q-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 28DFB185A791; Mon, 10 Jul 2023 19:49:08 +0000 (UTC) Received: from llong.com (unknown [10.22.18.171]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4D32F111E3E6; Mon, 10 Jul 2023 19:49:07 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Josh Poimboeuf , Pawan Gupta , Jacob Pan , Len Brown , Jonathan Corbet , "Rafael J . Wysocki" Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, x86@kernel.org, linux-pm@vger.kernel.org, Robin Jarry , Joe Mario , Randy Dunlap , Waiman Long Subject: [PATCH v5 1/4] x86/speculation: Add __update_spec_ctrl() helper Date: Mon, 10 Jul 2023 15:48:54 -0400 Message-Id: <20230710194857.2898284-2-longman@redhat.com> In-Reply-To: <20230710194857.2898284-1-longman@redhat.com> References: <20230710194857.2898284-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Add a new __update_spec_ctrl() helper which is a variant of update_spec_ctrl() that can be used in a noinstr function. Suggested-by: Peter Zijlstra Signed-off-by: Waiman Long Acked-by: Rafael J. Wysocki --- arch/x86/include/asm/nospec-branch.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 55388c9f7601..06ceacfd1fe2 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -9,7 +9,7 @@ #include #include -#include +#include #include #include #include @@ -488,6 +488,16 @@ DECLARE_PER_CPU(u64, x86_spec_ctrl_current); extern void update_spec_ctrl_cond(u64 val); extern u64 spec_ctrl_current(void); +/* + * This can be used in noinstr function & should only be called in bare + * metal context. + */ +static __always_inline void __update_spec_ctrl(u64 val) +{ + __this_cpu_write(x86_spec_ctrl_current, val); + native_wrmsrl(MSR_IA32_SPEC_CTRL, val); +} + /* * With retpoline, we must use IBRS to restrict branch prediction * before calling into firmware. From patchwork Mon Jul 10 19:48:55 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 13307547 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 53782C001B0 for ; Mon, 10 Jul 2023 19:50:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229741AbjGJTur (ORCPT ); Mon, 10 Jul 2023 15:50:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51456 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229659AbjGJTuq (ORCPT ); Mon, 10 Jul 2023 15:50:46 -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 94827198 for ; Mon, 10 Jul 2023 12:49:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1689018553; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=V8XTPlLt8h9osvtrHWj/nnm4IOfNvjA5a3kfsjNIri8=; b=Jby9KlBji81KmIWc8EF2sc2Paw6h71RZpB6d6C9+5n+grglaAVSLlwna1MpVlWjeml1ffM mINKJQTCAxICVuhfU1Yj9dLKnj+5DCTWPlSrhMGdWM6MbTruLOBGhb+x9UvToT1j7n9EL5 5LzewMpn8r4pYi716zLnVquI9eoLBKk= 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-449-cOWTCb-nMjCc6MG-0HCf_A-1; Mon, 10 Jul 2023 15:49:09 -0400 X-MC-Unique: cOWTCb-nMjCc6MG-0HCf_A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 1A10F104458F; Mon, 10 Jul 2023 19:49:09 +0000 (UTC) Received: from llong.com (unknown [10.22.18.171]) by smtp.corp.redhat.com (Postfix) with ESMTP id 38CC4111E3E6; Mon, 10 Jul 2023 19:49:08 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Josh Poimboeuf , Pawan Gupta , Jacob Pan , Len Brown , Jonathan Corbet , "Rafael J . Wysocki" Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, x86@kernel.org, linux-pm@vger.kernel.org, Robin Jarry , Joe Mario , Randy Dunlap , Waiman Long Subject: [PATCH v5 2/4] x86/idle: Disable IBRS when cpu is offline Date: Mon, 10 Jul 2023 15:48:55 -0400 Message-Id: <20230710194857.2898284-3-longman@redhat.com> In-Reply-To: <20230710194857.2898284-1-longman@redhat.com> References: <20230710194857.2898284-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org 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 Acked-by: Rafael J. Wysocki --- arch/x86/kernel/smpboot.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index e1aa2cd7734b..68e2e044ab8b 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -87,6 +87,7 @@ #include #include #include +#include /* representing HT siblings of each logical CPU */ DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map); @@ -1743,8 +1744,15 @@ void __noreturn hlt_play_dead(void) native_halt(); } +/* + * native_play_dead() is essentially a __noreturn function, but it can't + * be marked as such as the compiler may complain about it. + */ void native_play_dead(void) { + if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS)) + __update_spec_ctrl(0); + play_dead_common(); tboot_shutdown(TB_SHUTDOWN_WFS); From patchwork Mon Jul 10 19:48:56 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 13307546 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 4C5D4EB64DA for ; Mon, 10 Jul 2023 19:50:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229946AbjGJTum (ORCPT ); Mon, 10 Jul 2023 15:50:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51542 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229732AbjGJTul (ORCPT ); Mon, 10 Jul 2023 15:50:41 -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 B731D19C for ; Mon, 10 Jul 2023 12:49:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1689018556; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=a28aXvRJ7amV1kNyaLXIB+aU7kYRY1GTXEf8SQiQifs=; b=VaAyzkSDFZehaoAj/COBJhQrzD97pmsPdUYz+TAfalmpTM2QnspmmhhpkA/rr+HdhiP7AW 933qS708HjEloTL69tw/FEGyWrnJahZRggEpgvE/JvePTNlpsLcqSCSTGYfzbwSG4i+eRu WU1KiZ22QsDgfKnJtv+mV+/K/xzb3a4= 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-656-GDihBXQ8Otyp4A0BaShv8g-1; Mon, 10 Jul 2023 15:49:10 -0400 X-MC-Unique: GDihBXQ8Otyp4A0BaShv8g-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 08004800193; Mon, 10 Jul 2023 19:49:10 +0000 (UTC) Received: from llong.com (unknown [10.22.18.171]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2A1A9111E3E6; Mon, 10 Jul 2023 19:49:09 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Josh Poimboeuf , Pawan Gupta , Jacob Pan , Len Brown , Jonathan Corbet , "Rafael J . Wysocki" Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, x86@kernel.org, linux-pm@vger.kernel.org, Robin Jarry , Joe Mario , Randy Dunlap , Waiman Long Subject: [PATCH v5 3/4] intel_idle: Use __update_spec_ctrl() in intel_idle_ibrs() Date: Mon, 10 Jul 2023 15:48:56 -0400 Message-Id: <20230710194857.2898284-4-longman@redhat.com> In-Reply-To: <20230710194857.2898284-1-longman@redhat.com> References: <20230710194857.2898284-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org When intel_idle_ibrs() is called, it modifies the SPEC_CTRL MSR to 0 in order disable IBRS. However, the new MSR value isn't reflected in x86_spec_ctrl_current which is at odd with the other code that keep track of its state in that percpu variable. Use the new __update_spec_ctrl() to have the x86_spec_ctrl_current percpu value properly updated. Signed-off-by: Waiman Long Acked-by: Rafael J. Wysocki --- drivers/idle/intel_idle.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c index b930036edbbe..c9479f089037 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -182,12 +182,12 @@ static __cpuidle int intel_idle_ibrs(struct cpuidle_device *dev, int ret; if (smt_active) - native_wrmsrl(MSR_IA32_SPEC_CTRL, 0); + __update_spec_ctrl(0); ret = __intel_idle(dev, drv, index); if (smt_active) - native_wrmsrl(MSR_IA32_SPEC_CTRL, spec_ctrl); + __update_spec_ctrl(spec_ctrl); return ret; } From patchwork Mon Jul 10 19:48:57 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 13307548 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 CE0D2C001DC for ; Mon, 10 Jul 2023 19:50:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231448AbjGJTuu (ORCPT ); Mon, 10 Jul 2023 15:50:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51548 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231361AbjGJTut (ORCPT ); Mon, 10 Jul 2023 15:50:49 -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 EF2651AA for ; Mon, 10 Jul 2023 12:49:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1689018557; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zVD0BJNeNWCX3FiC5d0xpNwjoMoIZh8smCbpmvPkLpA=; b=ewijZuS5uksptzthR2NSqTy3dCYt+wZmohfpmEEzsVa8KM3hNUA8w49agAhZPiMJI4ieZr yMDDMtVCttKtPWghyKFNfhkf9OLlHnjZEUc63gJuyWy9oZQ8NywbD+OBKY4P1aWW6iN5jk d7rq01a58GQl3nhV4PAfMqljqvGifQA= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-335-8AR2pWZvNKWB2zwIf0sXOg-1; Mon, 10 Jul 2023 15:49:13 -0400 X-MC-Unique: 8AR2pWZvNKWB2zwIf0sXOg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E79D73C11CC7; Mon, 10 Jul 2023 19:49:10 +0000 (UTC) Received: from llong.com (unknown [10.22.18.171]) by smtp.corp.redhat.com (Postfix) with ESMTP id 17B72111E3E6; Mon, 10 Jul 2023 19:49:10 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Josh Poimboeuf , Pawan Gupta , Jacob Pan , Len Brown , Jonathan Corbet , "Rafael J . Wysocki" Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, x86@kernel.org, linux-pm@vger.kernel.org, Robin Jarry , Joe Mario , Randy Dunlap , Waiman Long Subject: [PATCH v5 4/4] intel_idle: Add ibrs_off module parameter to force disable IBRS Date: Mon, 10 Jul 2023 15:48:57 -0400 Message-Id: <20230710194857.2898284-5-longman@redhat.com> In-Reply-To: <20230710194857.2898284-1-longman@redhat.com> References: <20230710194857.2898284-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Commit bf5835bcdb96 ("intel_idle: Disable IBRS during long idle") disables IBRS when the cstate is 6 or lower. However, there are some use cases where a customer may want to use max_cstate=1 to lower latency. Such use cases will suffer from the performance degradation caused by the enabling of IBRS in the sibling idle thread. Add a "ibrs_off" module parameter to force disable IBRS and the CPUIDLE_FLAG_IRQ_ENABLE flag if set. In the case of a Skylake server with max_cstate=1, this new ibrs_off option will likely increase the IRQ response latency as IRQ will now be disabled. When running SPECjbb2015 with cstates set to C1 on a Skylake system. First test when the kernel is booted with: "intel_idle.ibrs_off" max-jOPS = 117828, critical-jOPS = 66047 Then retest when the kernel is booted without the "intel_idle.ibrs_off" added. max-jOPS = 116408, critical-jOPS = 58958 That means booting with "intel_idle.ibrs_off" improves performance by: max-jOPS: 1.2%, which could be considered noise range. critical-jOPS: 12%, which is definitely a solid improvement. The admin-guide/pm/intel_idle.rst file is updated to add a description about the new "ibrs_off" module parameter. Signed-off-by: Waiman Long Acked-by: Rafael J. Wysocki Tested-by: Robin Jarry --- Documentation/admin-guide/pm/intel_idle.rst | 17 ++++++++++++++++- drivers/idle/intel_idle.c | 11 ++++++++++- 2 files changed, 26 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst index b799a43da62e..39bd6ecce7de 100644 --- a/Documentation/admin-guide/pm/intel_idle.rst +++ b/Documentation/admin-guide/pm/intel_idle.rst @@ -170,7 +170,7 @@ and ``idle=nomwait``. If any of them is present in the kernel command line, the ``MWAIT`` instruction is not allowed to be used, so the initialization of ``intel_idle`` will fail. -Apart from that there are four module parameters recognized by ``intel_idle`` +Apart from that there are five module parameters recognized by ``intel_idle`` itself that can be set via the kernel command line (they cannot be updated via sysfs, so that is the only way to change their values). @@ -216,6 +216,21 @@ are ignored). The idle states disabled this way can be enabled (on a per-CPU basis) from user space via ``sysfs``. +The ``ibrs_off`` module parameter is a boolean flag (defaults to +false). If set, it is used to control if IBRS (Indirect Branch Restricted +Speculation) should be turned off when the CPU enters an idle state. +This flag does not affect CPUs that use Enhanced IBRS which can remain +on with little performance impact. + +For some CPUs, IBRS will be selected as mitigation for Spectre v2 and Retbleed +security vulnerabilities by default. Leaving the IBRS mode on while idling may +have a performance impact on its sibling CPU. The IBRS mode will be turned off +by default when the CPU enters into a deep idle state, but not in some +shallower ones. Setting the ``ibrs_off`` module parameter will force the IBRS +mode to off when the CPU is in any one of the available idle states. This may +help performance of a sibling CPU at the expense of a slightly higher wakeup +latency for the idle CPU. + .. _intel-idle-core-and-package-idle-states: diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c index c9479f089037..e1b826344682 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -69,6 +69,7 @@ static int max_cstate = CPUIDLE_STATE_MAX - 1; static unsigned int disabled_states_mask __read_mostly; static unsigned int preferred_states_mask __read_mostly; static bool force_irq_on __read_mostly; +static bool ibrs_off __read_mostly; static struct cpuidle_device __percpu *intel_idle_cpuidle_devices; @@ -1919,11 +1920,13 @@ static void state_update_enter_method(struct cpuidle_state *state, int cstate) } if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) && - state->flags & CPUIDLE_FLAG_IBRS) { + ((state->flags & CPUIDLE_FLAG_IBRS) || ibrs_off)) { /* * IBRS mitigation requires that C-states are entered * with interrupts disabled. */ + if (ibrs_off && (state->flags & CPUIDLE_FLAG_IRQ_ENABLE)) + state->flags &= ~CPUIDLE_FLAG_IRQ_ENABLE; WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE); state->enter = intel_idle_ibrs; return; @@ -2346,3 +2349,9 @@ MODULE_PARM_DESC(preferred_cstates, "Mask of preferred idle states"); * 'CPUIDLE_FLAG_INIT_XSTATE' and 'CPUIDLE_FLAG_IBRS' flags. */ module_param(force_irq_on, bool, 0444); +/* + * Force the disabling of IBRS when X86_FEATURE_KERNEL_IBRS is on and + * CPUIDLE_FLAG_IRQ_ENABLE isn't set. + */ +module_param(ibrs_off, bool, 0444); +MODULE_PARM_DESC(ibrs_off, "Disable IBRS when idle");