From nobody Sun Feb 8 08:27:42 2026 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 00AEBC001DC for ; Thu, 27 Jul 2023 18:48:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231630AbjG0SsM (ORCPT ); Thu, 27 Jul 2023 14:48:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36322 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231367AbjG0Sr4 (ORCPT ); Thu, 27 Jul 2023 14:47:56 -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 639D730FB for ; Thu, 27 Jul 2023 11:46:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690483583; 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=a86H4y4z8KX0kr9JT7xslzvC5qr9VS6pS7JR1Mg/VpQ=; b=XSWv4PwruExlvuBPrkLTnHcKj94w7xSOUTfStWFFZ0W5IiOXynwGMKzq1bbAAFUxnm0BAZ a+S49kpfIo2j2jgYnr+b6UdLtiBBjE3lxwZlo4/M6zonn0dezaNDRM5UEtO+yPTSUaq/jT Ypv/1Uoyll6al8lgLjvNlQ928k0Ius0= 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-mjyQeE1zOLGs7AetcTKNHA-1; Thu, 27 Jul 2023 14:46:17 -0400 X-MC-Unique: mjyQeE1zOLGs7AetcTKNHA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 04B9888D518; Thu, 27 Jul 2023 18:46:17 +0000 (UTC) Received: from llong.com (unknown [10.22.17.17]) by smtp.corp.redhat.com (Postfix) with ESMTP id 371AFC57964; Thu, 27 Jul 2023 18:46:16 +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 v6 1/4] x86/speculation: Add __update_spec_ctrl() helper Date: Thu, 27 Jul 2023 14:45:57 -0400 Message-Id: <20230727184600.26768-2-longman@redhat.com> In-Reply-To: <20230727184600.26768-1-longman@redhat.com> References: <20230727184600.26768-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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/spec-ctrl.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/arch/x86/include/asm/spec-ctrl.h b/arch/x86/include/asm/spec-c= trl.h index cb0386fc4dc3..d03408e0468a 100644 --- a/arch/x86/include/asm/spec-ctrl.h +++ b/arch/x86/include/asm/spec-ctrl.h @@ -4,6 +4,7 @@ =20 #include #include +#include =20 /* * On VMENTER we must preserve whatever view of the SPEC_CTRL MSR @@ -76,6 +77,16 @@ static inline u64 ssbd_tif_to_amd_ls_cfg(u64 tifn) return (tifn & _TIF_SSBD) ? x86_amd_ls_cfg_ssbd_mask : 0ULL; } =20 +/* + * 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); +} + #ifdef CONFIG_SMP extern void speculative_store_bypass_ht_init(void); #else --=20 2.31.1 From nobody Sun Feb 8 08:27:42 2026 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 8CE9CC04A94 for ; Thu, 27 Jul 2023 18:47:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231184AbjG0SrV (ORCPT ); Thu, 27 Jul 2023 14:47:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36102 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231206AbjG0SrL (ORCPT ); Thu, 27 Jul 2023 14:47:11 -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 D984930E4 for ; Thu, 27 Jul 2023 11:46:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690483582; 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=p0Bv8RV/6VKQUXDLbsWN97ne3VW3ZcB7lEFXae7aK9U=; b=eLZt9X2NsG4bodWipo9HB5pdQxYTRZngVG4l+EjDKLiJYKZiay7yN/9erIx/2/osFDLTyk OpYQ8v9HmuKx2PR/rrv9j+GNjC8fxQ3H7uZ62t2sIpN05jnUzMFiigQol4PJd9ODNplfG/ 9d3QAlYdTzsYy1gKEM0JZ7le/vUUdsY= 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-501-8ItcYOwWMwCWW9Ry2Q2B5g-1; Thu, 27 Jul 2023 14:46:18 -0400 X-MC-Unique: 8ItcYOwWMwCWW9Ry2Q2B5g-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id DCEDA88D4E2; Thu, 27 Jul 2023 18:46:17 +0000 (UTC) Received: from llong.com (unknown [10.22.17.17]) by smtp.corp.redhat.com (Postfix) with ESMTP id 15228C57964; Thu, 27 Jul 2023 18:46:17 +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 v6 2/4] x86/idle: Disable IBRS when cpu is offline Date: Thu, 27 Jul 2023 14:45:58 -0400 Message-Id: <20230727184600.26768-3-longman@redhat.com> In-Reply-To: <20230727184600.26768-1-longman@redhat.com> References: <20230727184600.26768-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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..16f420d49a13 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -87,6 +87,7 @@ #include #include #include +#include =20 /* 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(); } =20 +/* + * 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); =20 --=20 2.31.1 From nobody Sun Feb 8 08:27:42 2026 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 7A088C00528 for ; Thu, 27 Jul 2023 18:48:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231414AbjG0SsI (ORCPT ); Thu, 27 Jul 2023 14:48:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36320 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231339AbjG0Sr4 (ORCPT ); Thu, 27 Jul 2023 14:47:56 -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 49DCE30ED for ; Thu, 27 Jul 2023 11:46:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690483582; 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=hgcVQqDmL6DGm3gA3jePiRRXjc2Eh2fCViWl8QhUEvg=; b=Y4JSd47Xegv6a1ISXruZJHB2sj7hoX9QuNgmxYMIM79hsCpnSlvmq09xjBZj5FCP8NSnZF zDrRpeDw8ZnEXg+wQNe7NsyvhU5L6dEWJC3HO/RHjcnLcqNhIIy+0gfXuiucEA8m58OdqC n8m2B+/3KsO2BIYEp/QpTNbE8ccwAKg= Received: from mimecast-mx02.redhat.com (66.187.233.73 [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-132-6W-bzWr5NiSbdIJR7bTk_Q-1; Thu, 27 Jul 2023 14:46:21 -0400 X-MC-Unique: 6W-bzWr5NiSbdIJR7bTk_Q-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C83183828890; Thu, 27 Jul 2023 18:46:18 +0000 (UTC) Received: from llong.com (unknown [10.22.17.17]) by smtp.corp.redhat.com (Postfix) with ESMTP id EB4A8C57964; Thu, 27 Jul 2023 18:46:17 +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 v6 3/4] intel_idle: Use __update_spec_ctrl() in intel_idle_ibrs() Date: Thu, 27 Jul 2023 14:45:59 -0400 Message-Id: <20230727184600.26768-4-longman@redhat.com> In-Reply-To: <20230727184600.26768-1-longman@redhat.com> References: <20230727184600.26768-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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. Since spec-ctrl.h includes both msr.h and nospec-branch.h, we can remove those from the include file list. Signed-off-by: Waiman Long Acked-by: Rafael J. Wysocki --- drivers/idle/intel_idle.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c index 256c2d42e350..d286f31a5b96 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -53,9 +53,8 @@ #include #include #include -#include #include -#include +#include #include =20 #define INTEL_IDLE_VERSION "0.5.1" @@ -182,12 +181,12 @@ static __cpuidle int intel_idle_ibrs(struct cpuidle_d= evice *dev, int ret; =20 if (smt_active) - native_wrmsrl(MSR_IA32_SPEC_CTRL, 0); + __update_spec_ctrl(0); =20 ret =3D __intel_idle(dev, drv, index); =20 if (smt_active) - native_wrmsrl(MSR_IA32_SPEC_CTRL, spec_ctrl); + __update_spec_ctrl(spec_ctrl); =20 return ret; } --=20 2.31.1 From nobody Sun Feb 8 08:27:42 2026 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 3310CC04A94 for ; Thu, 27 Jul 2023 18:47:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231209AbjG0Srz (ORCPT ); Thu, 27 Jul 2023 14:47:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36336 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230438AbjG0Srw (ORCPT ); Thu, 27 Jul 2023 14:47:52 -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 D4D513583 for ; Thu, 27 Jul 2023 11:46:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690483585; 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=2oZBMKFgh/k80R5zLXcqzyZRHBrniBdfNnHbJbBDWvA=; b=UawEtenqaaZy0q1brHG6NoQXcGwUqm4Ao4tNyee97hqUYanaiE/18vs7K71Hp3BcBkqmJG 0Ff/SGtPTBoyZbWzbMGvPtJhIjdWkTkrHB4S0Th8pphVAoudj7FZ6LewPv9XHWtzI9HC/o 7TwApsoNTCZjXN6VpEJMZGgzxNkrgJM= 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-182-xnim8OnLOHqLwceCVRzn7Q-1; Thu, 27 Jul 2023 14:46:20 -0400 X-MC-Unique: xnim8OnLOHqLwceCVRzn7Q-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A794388D4E2; Thu, 27 Jul 2023 18:46:19 +0000 (UTC) Received: from llong.com (unknown [10.22.17.17]) by smtp.corp.redhat.com (Postfix) with ESMTP id D6257C57966; Thu, 27 Jul 2023 18:46:18 +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 v6 4/4] intel_idle: Add ibrs_off module parameter to force disable IBRS Date: Thu, 27 Jul 2023 14:46:00 -0400 Message-Id: <20230727184600.26768-5-longman@redhat.com> In-Reply-To: <20230727184600.26768-1-longman@redhat.com> References: <20230727184600.26768-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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=3D1 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=3D1, 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 =3D 117828, critical-jOPS =3D 66047 Then retest when the kernel is booted without the "intel_idle.ibrs_off" added. max-jOPS =3D 116408, critical-jOPS =3D 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 --- 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/ad= min-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=3Dnomwait``. If any of them is present in t= he kernel command line, the ``MWAIT`` instruction is not allowed to be used, so the initialization of ``intel_idle`` will fail. =20 -Apart from that there are four module parameters recognized by ``intel_idl= e`` +Apart from that there are five module parameters recognized by ``intel_idl= e`` 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). =20 @@ -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``. =20 +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 Retb= leed +security vulnerabilities by default. Leaving the IBRS mode on while idlin= g may +have a performance impact on its sibling CPU. The IBRS mode will be turne= d 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 wake= up +latency for the idle CPU. + =20 .. _intel-idle-core-and-package-idle-states: =20 diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c index d286f31a5b96..18fa47370bde 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -68,6 +68,7 @@ static int max_cstate =3D 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; =20 static struct cpuidle_device __percpu *intel_idle_cpuidle_devices; =20 @@ -1852,11 +1853,13 @@ static void state_update_enter_method(struct cpuidl= e_state *state, int cstate) } =20 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 &=3D ~CPUIDLE_FLAG_IRQ_ENABLE; WARN_ON_ONCE(state->flags & CPUIDLE_FLAG_IRQ_ENABLE); state->enter =3D intel_idle_ibrs; return; @@ -2175,3 +2178,9 @@ MODULE_PARM_DESC(preferred_cstates, "Mask of preferre= d 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"); --=20 2.31.1