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=-8.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_NONE,USER_AGENT_SANE_1 autolearn=unavailable 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 B4EABC71156 for ; Thu, 3 Dec 2020 11:43:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5CE8A22201 for ; Thu, 3 Dec 2020 11:43:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388871AbgLCLn3 (ORCPT ); Thu, 3 Dec 2020 06:43:29 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:36416 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729054AbgLCLn1 (ORCPT ); Thu, 3 Dec 2020 06:43:27 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606995720; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=z2/JUVMbgmiwF4hVlwNNOMPd3HZB9sBekSW1KAEyKUo=; b=eAAGNo9jJ238Io+nRPRPr61HV0KhM0SVlgw9GYABCjWwhgKGjAxn0msKRo+bTtb41mN1Vz AUYZwgUoyuLtQ67MsVP7zAK4VneqO6P8/dftmdbZ1Kg1eCmQj2faSgksNbf5MZ74eZlbHg lNNtcoH/KoMy8Sii3naNm+sW/snz604= Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-488-ReZi_JZbPNewoeLWA89kdw-1; Thu, 03 Dec 2020 06:41:59 -0500 X-MC-Unique: ReZi_JZbPNewoeLWA89kdw-1 Received: by mail-ed1-f69.google.com with SMTP id z20so813980edl.21 for ; Thu, 03 Dec 2020 03:41:59 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=z2/JUVMbgmiwF4hVlwNNOMPd3HZB9sBekSW1KAEyKUo=; b=EDH21MkJJED5RhBYDYlNgCdnzKoZGhRZh05mxvgvVQXg1nz3i9cudzHw3HTalRrnNN VU3R7ybJfSgIglghwCT6/PLLu0t5LVnhii/1JaACrMugv3YCfgKgYQxrJ4Re+KAk/CtE bIkf34VIDqpY7OT9jJVD1mWczAFFRdfILPxuuGKVuR9eZWRCcar3OrQfTGtbCGTGFh1m wzW0t2m7/voJGagnOkmZ759d45yQ0vzzSJK0pYV3UiHDvG5aS5x5EmZOjNct9oqUfaLg 7wOktjcIbPXSfVIFXa7HhwWB2OcGZ9G/m8FnpT5TRO9Jzn2qSzyF8AnzrV4QQGTdN1sq nNzg== X-Gm-Message-State: AOAM531UmaA0ey/S74HgMqBEEu3gt/X/RQ2er9x1Smki3vtfToO2HFE7 8F6yMVJpulDCB3p/CB4KyiilPmJjGiJcYfRchaK0u6C+0I9G5UJIYrHIIqmOYyiHJpgtDAEMqY0 9nystnyw1dCSTtT/eyEm9p/E0 X-Received: by 2002:a17:906:2ec3:: with SMTP id s3mr2053811eji.133.1606995718240; Thu, 03 Dec 2020 03:41:58 -0800 (PST) X-Google-Smtp-Source: ABdhPJxW3JyLsSOLmxQokAFrQzTXTB6znHfAxgajBoxXmC9FZky84x7HveAqEGoG3zNV8WzQk1bLWw== X-Received: by 2002:a17:906:2ec3:: with SMTP id s3mr2053804eji.133.1606995718043; Thu, 03 Dec 2020 03:41:58 -0800 (PST) Received: from ?IPv6:2001:b07:6468:f312:c8dd:75d4:99ab:290a? ([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id z12sm677926ejr.17.2020.12.03.03.41.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 03 Dec 2020 03:41:57 -0800 (PST) Subject: Re: [PATCH 0/2] RFC: Precise TSC migration To: Thomas Gleixner , Maxim Levitsky , kvm@vger.kernel.org Cc: Oliver Upton , Ingo Molnar , Sean Christopherson , open list , Marcelo Tosatti , Jonathan Corbet , Wanpeng Li , Borislav Petkov , Jim Mattson , "H. Peter Anvin" , "open list:DOCUMENTATION" , Joerg Roedel , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Vitaly Kuznetsov References: <20201130133559.233242-1-mlevitsk@redhat.com> <87lfehfhez.fsf@nanos.tec.linutronix.de> From: Paolo Bonzini Message-ID: Date: Thu, 3 Dec 2020 12:41:56 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <87lfehfhez.fsf@nanos.tec.linutronix.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/12/20 20:35, Thomas Gleixner wrote: >> This makes the random error in calculation of this value invariant >> across vCPUS, and allows the guest to do kvmclock calculation in userspace >> (vDSO) since kvmclock parameters are vCPU invariant. > > That's not the case today? OMG! It's optional. If the host tells the guest that the host TSC is messed up, kvmclock disables its vDSO implementation and falls back to the syscall. Paolo