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=-2.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 0C448C65BAF for ; Wed, 12 Dec 2018 20:00:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B37912084E for ; Wed, 12 Dec 2018 20:00:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="As3SXsaJ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B37912084E 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 S1727157AbeLLUAR (ORCPT ); Wed, 12 Dec 2018 15:00:17 -0500 Received: from mail.skyhub.de ([5.9.137.197]:32964 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726242AbeLLUAQ (ORCPT ); Wed, 12 Dec 2018 15:00:16 -0500 Received: from zn.tnic (p200300EC2BCDD8007CFD4A6887308591.dip0.t-ipconnect.de [IPv6:2003:ec:2bcd:d800:7cfd:4a68:8730:8591]) (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 B1B191EC0B89; Wed, 12 Dec 2018 21:00:14 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1544644814; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=0sTvYlXu7v0gxztiS6M0w+P207TXjeReekhtCXgqiaU=; b=As3SXsaJ6zw/tRa5mkEL2GEH6Z7XNSgQRy0FkBXyYxXv2a15FEnLsx9h6+k15W5s2vNxEp HGkh0CgF/oa8Dz82VJARsz7F/0Q7xvr7bwnwPAGejRJtX5Z7JWd1nS10Vkd0DGl7z8+zjO QLZQ4l0uRCvT0Ef+GaD0aRkwKYjKHKg= Date: Wed, 12 Dec 2018 21:00:05 +0100 From: Borislav Petkov To: Andy Lutomirski Cc: Tom Lendacky , LKML , X86 ML , "H. Peter Anvin" , Josh Poimboeuf , Peter Zijlstra , John Stultz Subject: Re: [RFC PATCH 4/4] x86/TSC: Use RDTSCP Message-ID: <20181212200005.GF6653@zn.tnic> References: <20181211222326.14581-1-bp@alien8.de> <20181211222326.14581-5-bp@alien8.de> <59aad362-4a5b-dd8b-642f-0dc3f83cf7ee@amd.com> <20181211233901.GV27375@zn.tnic> <20181212100814.GB6653@zn.tnic> <20181212184459.GE6653@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 12, 2018 at 10:50:30AM -0800, Andy Lutomirski wrote: > As far as I know, RDTSCP gets the job done, as does LFENCE, RDTSC on > Intel. Same on AMD when LFENCE has been made dispatch-serializing. > There was a big discussion a few years ago where we changed it > from LFENCE;RDTSC;LFENCE to just LFENCE;RDTSC after everyone was > reasonably convinced that the uarch would not dispatch two RDTSCs > backwards if the first one was immediately preceeded by LFENCE. Yeah, the second one won't pass the LFENCE so you won't see time going backwards, sure. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.