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=-9.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT 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 C5773C6783B for ; Tue, 11 Dec 2018 22:23:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B9942084C for ; Tue, 11 Dec 2018 22:23:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="LNTpgDMY" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8B9942084C Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=alien8.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 S1726389AbeLKWXn (ORCPT ); Tue, 11 Dec 2018 17:23:43 -0500 Received: from mail.skyhub.de ([5.9.137.197]:46274 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726346AbeLKWXe (ORCPT ); Tue, 11 Dec 2018 17:23:34 -0500 Received: from zn.tnic (p200300EC2BCD2B0010F6E1EC68D6BA6C.dip0.t-ipconnect.de [IPv6:2003:ec:2bcd:2b00:10f6:e1ec:68d6:ba6c]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id DF11F1EC0C11; Tue, 11 Dec 2018 23:23:32 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1544567013; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GKywmujzPhFneQ5I17/1RpzWlb/UISTliKsdCm3/o3U=; b=LNTpgDMYzGmXbBMPkw4FU+nOeHJjP+76PyTeTXM6lG0VG/QcRnHBqPql5QgM3Vu4EpSGrR cNQekHLkZz3te/4omAgWnIBtNL6TILRDM9UCeHaSuY/kTTR/vbdOx1UyzQSBPZ9F0SVgkq /9NIm0Ecy+K3T3IEAFhZfVirZ+kJEyI= From: Borislav Petkov To: LKML Cc: X86 ML , Andy Lutomirski , "H. Peter Anvin" , Josh Poimboeuf , Peter Zijlstra , Tom Lendacky , Andy Lutomirski , John Stultz Subject: [RFC PATCH 4/4] x86/TSC: Use RDTSCP Date: Tue, 11 Dec 2018 23:23:26 +0100 Message-Id: <20181211222326.14581-5-bp@alien8.de> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20181211222326.14581-1-bp@alien8.de> References: <20181211222326.14581-1-bp@alien8.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Borislav Petkov Currently, the kernel uses [LM]FENCE; RDTSC in the timekeeping code, to guarantee monotonicity of time where the *FENCE is selected based on vendor. Replace that sequence with RDTSCP which is faster or on-par and gives the same guarantees. A microbenchmark on Intel shows that the change is on-par. On AMD, the change is either on-par with the current LFENCE-prefixed RDTSC and some are slightly better with RDTSCP. The comparison is done with the LFENCE-prefixed RDTSC (and not with the MFENCE-prefixed one, as one would normally expect) because all modern AMD families make LFENCE serializing and thus avoid the heavy MFENCE by effectively enabling X86_FEATURE_LFENCE_RDTSC. Co-developed-by: Thomas Gleixner Signed-off-by: Thomas Gleixner Signed-off-by: Borislav Petkov Cc: Tom Lendacky Cc: Andy Lutomirski Cc: "H. Peter Anvin" Cc: John Stultz Cc: x86@kernel.org Link: https://lkml.kernel.org/r/20181119184556.11479-1-bp@alien8.de --- arch/x86/include/asm/msr.h | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h index 91e4cf189914..5cc3930cb465 100644 --- a/arch/x86/include/asm/msr.h +++ b/arch/x86/include/asm/msr.h @@ -217,6 +217,8 @@ static __always_inline unsigned long long rdtsc(void) */ static __always_inline unsigned long long rdtsc_ordered(void) { + DECLARE_ARGS(val, low, high); + /* * The RDTSC instruction is not ordered relative to memory * access. The Intel SDM and the AMD APM are both vague on this @@ -227,9 +229,19 @@ static __always_inline unsigned long long rdtsc_ordered(void) * ordering guarantees as reading from a global memory location * that some other imaginary CPU is updating continuously with a * time stamp. + * + * Thus, use the preferred barrier on the respective CPU, aiming for + * RDTSCP as the default. */ - barrier_nospec(); - return rdtsc(); + asm volatile(ALTERNATIVE_3("rdtsc", + "mfence; rdtsc", X86_FEATURE_MFENCE_RDTSC, + "lfence; rdtsc", X86_FEATURE_LFENCE_RDTSC, + "rdtscp", X86_FEATURE_RDTSCP) + : EAX_EDX_RET(val, low, high) + /* RDTSCP clobbers ECX with MSR_TSC_AUX. */ + :: "ecx"); + + return EAX_EDX_VAL(val, low, high); } static inline unsigned long long native_read_pmc(int counter) -- 2.19.1