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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 866ECC4167B for ; Tue, 8 Dec 2020 09:49:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D05B23A82 for ; Tue, 8 Dec 2020 09:49:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728511AbgLHJtO (ORCPT ); Tue, 8 Dec 2020 04:49:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50582 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728028AbgLHJtN (ORCPT ); Tue, 8 Dec 2020 04:49:13 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C952C061749; Tue, 8 Dec 2020 01:48:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=7bcvgstjEVppk7+MPyrtpEwXq1xns69yzQtxAznXpyE=; b=SkHw+uYjKNb2aRytJV+52kzv2l MvuPXaK9BuESM9VjTmzXK7/dz2iUL0/CKuWMcKZ6ylR9V4qTU7kKLJA5oLvopX9zlQZ4lr/4q0pxn pJ5DFi/Q9r5l3f8IE+PuhxpAgDXnh+rvAvTG3y8cWw1EoGb8l8jrm8Naru/+2I2BcKHaoig27oXck b5//ZGMl6IejdckF35Y9xfmYGwR5VzWAxWNuFGEd8GaLJUYm5QLsYd/K0V235dnZSO3q0PLZd8f0n huBpRfNObPAfLG2WG+A+Ez5TyuQpzHN9KZtrerHlyJ8KCFiD1PqDgzYQIE1W6V457XeIvQmtI4iQr +aaB37sA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kmZbQ-0002Bc-38; Tue, 08 Dec 2020 09:48:12 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 91DA7304BAE; Tue, 8 Dec 2020 10:48:09 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7B47720812B43; Tue, 8 Dec 2020 10:48:09 +0100 (CET) Date: Tue, 8 Dec 2020 10:48:09 +0100 From: Peter Zijlstra To: Thomas Gleixner Cc: Vitaly Kuznetsov , Maxim Levitsky , "H. Peter Anvin" , Paolo Bonzini , Jonathan Corbet , Jim Mattson , Wanpeng Li , "open list:KERNEL SELFTEST FRAMEWORK" , Marcelo Tosatti , Sean Christopherson , open list , Ingo Molnar , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Joerg Roedel , Borislav Petkov , Shuah Khan , Andrew Jones , Oliver Upton , "open list:DOCUMENTATION" , kvm@vger.kernel.org Subject: Re: [PATCH v2 1/3] KVM: x86: implement KVM_{GET|SET}_TSC_STATE Message-ID: <20201208094809.GT2414@hirez.programming.kicks-ass.net> References: <20201203171118.372391-1-mlevitsk@redhat.com> <20201203171118.372391-2-mlevitsk@redhat.com> <87a6uq9abf.fsf@nanos.tec.linutronix.de> <1dbbeefc7c76c259b55582468ccd3aab35a6de60.camel@redhat.com> <87im9dlpsw.fsf@vitty.brq.redhat.com> <875z5d5x9m.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <875z5d5x9m.fsf@nanos.tec.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 07, 2020 at 06:41:41PM +0100, Thomas Gleixner wrote: > Right this happens still occasionally, but for quite some time this is > 100% firmware sillyness and not a fundamental property of the hardware > anymore. Ever since Nehalem (2008) TSC is synchronized on <= 2 sockets, and any observed deviation is firmware fail. I don't remember exactly where 4 socket and up got reliable. (there's the physical hotplug case, but let's not make this complicated) AMD has had Constant TSC since Barcelona which is roughly the same timeframe IIRC. So basically every TSC fail in the last decase is due to firmware being shit.