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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 AE2E4C4361B for ; Fri, 11 Dec 2020 00:30:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CF9C2312A for ; Fri, 11 Dec 2020 00:30:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393606AbgLKA3M (ORCPT ); Thu, 10 Dec 2020 19:29:12 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:28597 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2393103AbgLKA3F (ORCPT ); Thu, 10 Dec 2020 19:29:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1607646458; 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: in-reply-to:in-reply-to:references:references; bh=smSusb6V6UpqcgwJnIn5HTzBcj5wuKKaCTquGzVm8wA=; b=AG06PKhsVgS6RkQgk0Ey2XiA6kscOKzqC1jU06IgO14t4VfFtov8EeJoC3du8Tu3QXSDI+ M9DgTlwkHO4DFurDlbCEMdq0ZPwJO73ShfptWKEuOPeG9Gkvgy0BJNeuhufnftbSe0bUOE 6MJrK3FXTMrQE7rXTH9Ru4eyVtqm/IU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-545-01-RlXyYP0eRgWNEySdgJA-1; Thu, 10 Dec 2020 19:27:37 -0500 X-MC-Unique: 01-RlXyYP0eRgWNEySdgJA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 70D00180A086; Fri, 11 Dec 2020 00:27:34 +0000 (UTC) Received: from fuller.cnet (ovpn-112-7.gru2.redhat.com [10.97.112.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DB44A100239F; Fri, 11 Dec 2020 00:27:32 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id BFCF94172EDF; Thu, 10 Dec 2020 21:27:03 -0300 (-03) Date: Thu, 10 Dec 2020 21:27:03 -0300 From: Marcelo Tosatti To: Thomas Gleixner Cc: Maxim Levitsky , kvm@vger.kernel.org, "H. Peter Anvin" , Paolo Bonzini , Jonathan Corbet , Jim Mattson , Wanpeng Li , "open list:KERNEL SELFTEST FRAMEWORK" , Vitaly Kuznetsov , 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" Subject: Re: [PATCH v2 1/3] KVM: x86: implement KVM_{GET|SET}_TSC_STATE Message-ID: <20201211002703.GA47016@fuller.cnet> References: <20201203171118.372391-2-mlevitsk@redhat.com> <20201207232920.GD27492@fuller.cnet> <05aaabedd4aac7d3bce81d338988108885a19d29.camel@redhat.com> <87sg8g2sn4.fsf@nanos.tec.linutronix.de> <20201208181107.GA31442@fuller.cnet> <875z5c2db8.fsf@nanos.tec.linutronix.de> <20201209163434.GA22851@fuller.cnet> <87r1nyzogg.fsf@nanos.tec.linutronix.de> <20201210152618.GB23951@fuller.cnet> <87zh2lib8l.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87zh2lib8l.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Thu, Dec 10, 2020 at 10:48:10PM +0100, Thomas Gleixner wrote: > On Thu, Dec 10 2020 at 12:26, Marcelo Tosatti wrote: > > On Wed, Dec 09, 2020 at 09:58:23PM +0100, Thomas Gleixner wrote: > >> Marcelo, > >> > >> On Wed, Dec 09 2020 at 13:34, Marcelo Tosatti wrote: > >> > On Tue, Dec 08, 2020 at 10:33:15PM +0100, Thomas Gleixner wrote: > >> >> On Tue, Dec 08 2020 at 15:11, Marcelo Tosatti wrote: > >> >> > max_cycles overflow. Sent a message to Maxim describing it. > >> >> > >> >> Truly helpful. Why the hell did you not talk to me when you ran into > >> >> that the first time? > >> > > >> > Because > >> > > >> > 1) Users wanted CLOCK_BOOTTIME to stop counting while the VM > >> > is paused (so we wanted to stop guest clock when VM is paused anyway). > >> > >> How is that supposed to work w/o the guest kernels help if you have to > >> keep clock realtime up to date? > > > > Upon VM resume, we notify NTP daemon in the guest to sync realtime > > clock. > > Brilliant. What happens if there is no NTP daemon? What happens if the > NTP daemon is not part of the virt orchestration magic and cannot be > notified, then it will notice the time jump after the next update > interval. > > What about correctness? > > ALL CLOCK_* stop and resume when the VM is resumed at the point where > they stopped. > > So up to the point where NTP catches up and corrects clock realtime and > TAI other processes can observe that time jumped in the outside world, > e.g. via a network packet or whatever, but there is no reason why time > should have jumped outside vs. the local one. > > You really all live in a seperate universe creating your own rules how > things which other people work hard on to get it correct can be screwed > over. 1. T = read timestamp. 2. migrate (VM stops for a certain period). 3. use timestamp T. > Of course this all is nowhere documented in detail. At least a quick > search with about 10 different keyword combinations revealed absolutely > nothing. > > This features first, correctness later frenzy is insane and it better > stops now before you pile even more crap on the existing steaming pile > of insanities. Sure.