From patchwork Thu Jul 27 18:45:57 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 708388 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 10296C001DC for ; Thu, 27 Jul 2023 18:47:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230523AbjG0SrJ (ORCPT ); Thu, 27 Jul 2023 14:47:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36080 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230414AbjG0SrH (ORCPT ); Thu, 27 Jul 2023 14:47:07 -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 EE85430D4 for ; Thu, 27 Jul 2023 11:46:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690483581; 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=OEKUCFLQk7Dh6GhDnZyDXMbLDpzaV0w7rEB8bU7we001WN7YwYjq4nAo2HLbMxR30OQ8WA BwGoVxlAD2yV/acQY0Z8VZeM5tqSAXtbfD5IfG0Q/0Yr7xohcbak6IdLz7lOsqeeDf2Kbu 6cF47LVaCXKfPWeMJDtAn1/miFIxCjM= 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 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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/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-ctrl.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 @@ #include #include +#include /* * 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; } +/* + * 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 From patchwork Thu Jul 27 18:45:58 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 707442 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 2766CC001DC for ; Thu, 27 Jul 2023 18:47:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231129AbjG0Srw (ORCPT ); Thu, 27 Jul 2023 14:47:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36334 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230497AbjG0Srv (ORCPT ); Thu, 27 Jul 2023 14:47:51 -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 C329B3580 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=p0Bv8RV/6VKQUXDLbsWN97ne3VW3ZcB7lEFXae7aK9U=; b=TJU8Ulem51+qY16NQR+MWbBenLFlNTouE518p4kktBbTdiVaBOreirSzzCQUaY1WNFgnIs 5aBpQlMmSvlUrx8ljJVIvh2YJ386C2E6Bat8xE1vuazwBtjglEah/Ga1v+u2Zyw1+PFi9/ eTuSuzhv+rywPnL8+ZqtVRxb3+xssd8= 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 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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..16f420d49a13 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 Thu Jul 27 18:45:59 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 708387 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 B5C00C41513 for ; Thu, 27 Jul 2023 18:48:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231253AbjG0SsF (ORCPT ); Thu, 27 Jul 2023 14:48:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36340 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231378AbjG0Sr5 (ORCPT ); Thu, 27 Jul 2023 14:47:57 -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 115A43588 for ; Thu, 27 Jul 2023 11:46:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690483587; 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=XDAtWXIa/3H5gQu7ssCi4uVfnoNReHnpMERHsOMItkhfYRuc8mapNbLNrkbGJdj4n3JiKw BijaLqZFyTOZw2d3WjL5Hx3nqJMUrD1nggkyld5hPGAxLcD13ut7+SxTdCNAfjHMrUKY30 ZWGNz1YEML27q8FpCpqWA37qMXaa3S0= 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 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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. 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 #define INTEL_IDLE_VERSION "0.5.1" @@ -182,12 +181,12 @@ 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 Thu Jul 27 18:46:00 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 707441 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 EC2EAC04A94 for ; Thu, 27 Jul 2023 18:48:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231515AbjG0SsG (ORCPT ); Thu, 27 Jul 2023 14:48:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231296AbjG0Sr4 (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 380E130EB 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=2oZBMKFgh/k80R5zLXcqzyZRHBrniBdfNnHbJbBDWvA=; b=YX8r5I+oUwvPAB6WKdI2kW7EfK7HCpxTewdBgSnp9VKwIowUU5t7bWe+IP48WcuzSQlFsu Ds6UMLQtjLIlhX5PnxNfQOK6HOV/1LpVDdJ2L7eGotRh1SXsbJl1z3akDlzpYPlcfwfcv3 ZCoMeIg3eTziQXVue5EgIPPwvn/LBN4= 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 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 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 --- 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 d286f31a5b96..18fa47370bde 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -68,6 +68,7 @@ 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; @@ -1852,11 +1853,13 @@ 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; @@ -2175,3 +2178,9 @@ 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");