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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2DB4EC43441 for ; Sun, 25 Nov 2018 18:58:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EB53D2084E for ; Sun, 25 Nov 2018 18:58:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB53D2084E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727347AbeKZFtN (ORCPT ); Mon, 26 Nov 2018 00:49:13 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:52879 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727301AbeKZFtM (ORCPT ); Mon, 26 Nov 2018 00:49:12 -0500 Received: from localhost ([127.0.0.1] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1gQzax-0003SQ-Uk; Sun, 25 Nov 2018 19:57:28 +0100 Message-Id: <20181125185005.374062201@linutronix.de> User-Agent: quilt/0.65 Date: Sun, 25 Nov 2018 19:33:48 +0100 From: Thomas Gleixner To: LKML Cc: x86@kernel.org, Peter Zijlstra , Andy Lutomirski , Linus Torvalds , Jiri Kosina , Tom Lendacky , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Tim Chen , Andi Kleen , Dave Hansen , Casey Schaufler , Asit Mallick , Arjan van de Ven , Jon Masters , Waiman Long , Greg KH , Dave Stewart , Kees Cook Subject: [patch V2 20/28] x86/speculation: Avoid __switch_to_xtra() calls References: <20181125183328.318175777@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline; filename=x86-speculation-Avoid-switch-to-xtra-calls.patch Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The TIF_SPEC_IB bit does not need to be evaluated in the decision to invoke __switch_to_xtra() when: - CONFIG_SMP is disabled - The conditional STIPB mode is disabled The TIF_SPEC_IB bit still controls IBPB in both cases so the TIF work mask checks might invoke __switch_to_xtra() for nothing if TIF_SPEC_IB is the only set bit in the work masks. Optimize it out by masking the bit at compile time for CONFIG_SMP=n and at run time when the static key controlling the conditional STIBP mode is disabled. Signed-off-by: Thomas Gleixner --- arch/x86/include/asm/thread_info.h | 13 +++++++++++-- arch/x86/kernel/process.h | 15 +++++++++++++++ 2 files changed, 26 insertions(+), 2 deletions(-) --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -147,9 +147,18 @@ struct thread_info { _TIF_FSCHECK) /* flags to check in __switch_to() */ -#define _TIF_WORK_CTXSW \ +#define _TIF_WORK_CTXSW_BASE \ (_TIF_IO_BITMAP|_TIF_NOCPUID|_TIF_NOTSC|_TIF_BLOCKSTEP| \ - _TIF_SSBD|_TIF_SPEC_IB) + _TIF_SSBD) + +/* + * Avoid calls to __switch_to_xtra() on UP as STIBP is not evaluated. + */ +#ifdef CONFIG_SMP +# define _TIF_WORK_CTXSW (_TIF_WORK_CTXSW_BASE | _TIF_SPEC_IB) +#else +# define _TIF_WORK_CTXSW (_TIF_WORK_CTXSW_BASE) +#endif #define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY) #define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW) --- a/arch/x86/kernel/process.h +++ b/arch/x86/kernel/process.h @@ -2,6 +2,8 @@ // // Code shared between 32 and 64 bit +#include + void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p); /* @@ -14,6 +16,19 @@ static inline void switch_to_extra(struc unsigned long next_tif = task_thread_info(next)->flags; unsigned long prev_tif = task_thread_info(prev)->flags; + if (IS_ENABLED(CONFIG_SMP)) { + /* + * Avoid __switch_to_xtra() invocation when conditional + * STIPB is disabled and the only different bit is + * TIF_SPEC_IB. For CONFIG_SMP=n TIF_SPEC_IB is not + * in the TIF_WORK_CTXSW masks. + */ + if (!static_branch_likely(&switch_to_cond_stibp)) { + prev_tif &= ~_TIF_SPEC_IB; + next_tif &= ~_TIF_SPEC_IB; + } + } + /* * __switch_to_xtra() handles debug registers, i/o bitmaps, * speculation mitigations etc.