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 4A0A3C433FE for ; Wed, 9 Dec 2020 20:59:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1357B23D23 for ; Wed, 9 Dec 2020 20:59:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732037AbgLIU7G (ORCPT ); Wed, 9 Dec 2020 15:59:06 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:49336 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726501AbgLIU7G (ORCPT ); Wed, 9 Dec 2020 15:59:06 -0500 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1607547503; 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=U8FXkEeLmw4j1ELROJYnBZRGobC61UbHYQBmnv42St8=; b=fwE70pYwh2irwmwye2/3/Z34cz2hThNe+ULaC9eo2FGfieOgkb89CdwAi3x0fYvhlf3Ou4 mYWRrOsdlmF5zj5vi8mokDrqWSblAl/mrVGCJUi4JBDVTN3SMiSVM+WpNOd5woQXyiDieN hLFCjiN6nri5od9k5b4g4TVRhu6oIaAAScpuFXyyvjgkMozsDZXxN72YNyOkJcuHfXnD88 5wJul+IQfljI2YnFlQtP6GoZSW73FMATu4Yes0wkHEspqE/Svs6x2ljDq5Yru/2q3Q22Ac gj+SvwzADuANXLa2OpSYhatT/jb56ictDYI3iygTZxqy5R6BLUVT4OC8wXXmQA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1607547503; 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=U8FXkEeLmw4j1ELROJYnBZRGobC61UbHYQBmnv42St8=; b=f4NE+mMs/ZqUUwRSXrP7yHu0BlPfcW+WM93A0rcst4gtUNAmF2pEncgBHUV2Qd4+bA2m26 KFfU0BOrLpgo2dDg== To: Marcelo Tosatti 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 In-Reply-To: <20201209163434.GA22851@fuller.cnet> References: <20201203171118.372391-1-mlevitsk@redhat.com> <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> Date: Wed, 09 Dec 2020 21:58:23 +0100 Message-ID: <87r1nyzogg.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > 2) The solution to inject NMIs to the guest seemed overly > complicated. Why do you need NMIs? All you need is a way to communicate to the guest that it should prepare for clock madness to happen. Whether that's an IPI or a bit in a hyperpage which gets checked during the update of the guest timekeeping does not matter at all. But you certainly do not need an NMI because there is nothing useful you can do within an NMI. Thanks, tglx