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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BB470C433FE for ; Thu, 10 Nov 2022 18:22:30 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1otCBK-0007Sx-RJ; Thu, 10 Nov 2022 13:21:42 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1otCB9-0007SB-RT for qemu-devel@nongnu.org; Thu, 10 Nov 2022 13:21:34 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1otCB7-0003bx-G9 for qemu-devel@nongnu.org; Thu, 10 Nov 2022 13:21:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668104487; h=from:from:reply-to: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=Dye2HRqbYklepOdnOZpCyEOOQfq7ul1v9T1uXSZOlaE=; b=bO10ywxQA5AKDtm4xsUn6O35W/+70yrMX4SginWXL1V56AtprUAtX6QFxqQcxtNVdki/ZY nWchcuAUQOMJoBhEZFOZlFWCwWlAE+hQr/4yGPJKXdZGzROODctzMsKFWBt5nWImLpvKZx eaH2xUam6kTpMIxn0Ppddtb8b4PTUTs= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-255-EEd0P7xqN1WfI3vY9l1JMg-1; Thu, 10 Nov 2022 13:21:23 -0500 X-MC-Unique: EEd0P7xqN1WfI3vY9l1JMg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E27E7101A54E; Thu, 10 Nov 2022 18:21:22 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.115]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CD788C15BA8; Thu, 10 Nov 2022 18:21:18 +0000 (UTC) Date: Thu, 10 Nov 2022 18:21:15 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Michael S. Tsirkin" Cc: Igor Mammedov , qemu-devel@nongnu.org, Laurent Vivier , Richard Henderson , Ani Sinha , Thomas Huth , Paolo Bonzini , Eduardo Habkost , Marcel Apfelbaum , "Richard W.M. Jones" Subject: Re: [PATCH 0/4] hw: make TCO watchdog actually work by default for Q35 Message-ID: References: <20221031131934.425448-1-berrange@redhat.com> <20221031114835-mutt-send-email-mst@kernel.org> <20221101135724.7f89868c@fedora> <20221110112700-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20221110112700-mutt-send-email-mst@kernel.org> User-Agent: Mutt/2.2.7 (2022-08-07) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, Nov 10, 2022 at 11:29:21AM -0500, Michael S. Tsirkin wrote: > On Tue, Nov 01, 2022 at 01:03:17PM +0000, Daniel P. Berrangé wrote: > > On Tue, Nov 01, 2022 at 01:57:24PM +0100, Igor Mammedov wrote: > > > On Mon, 31 Oct 2022 11:48:58 -0400 > > > "Michael S. Tsirkin" wrote: > > > > > > > On Mon, Oct 31, 2022 at 01:50:24PM +0000, Daniel P. Berrangé wrote: > > > > > On Mon, Oct 31, 2022 at 01:19:30PM +0000, Daniel P. Berrangé wrote: > > > > > > The TCO watchdog is unconditionally integrated into the Q35 machine > > > > > > type by default, but at the same time is unconditionally disabled > > > > > > from firing by a host config option that overrides guest OS attempts > > > > > > to enable it. People have to know to set a magic -global to make > > > > > > it non-broken > > > > > > > > > > Incidentally I found that originally the TCO watchdog was not > > > > > unconditionally enabled. Its exposure to the guest could be > > > > > turned on/off using > > > > > > > > > > -global ICH9-LPC.enable_tco=bool > > > > > > > > > > This was implemented for machine type compat, but it also gave > > > > > apps a way to disable the watchdog functionality. Unfortunately > > > > > that ability was discarded in this series: > > > > > > > > > > https://lore.kernel.org/all/1453564933-29638-1-git-send-email-ehabkost@redhat.com/ > > > > > > > > > > but the 'enable_tco' property still exists in QOM, but silently > > > > > ignored. > > > > > > > > > > Seems we should either fix the impl of 'enable_tco', or remove the > > > > > QOM property entirely, so we don't pretend it can be toggled anymore. > > > > > > > > > > With regards, > > > > > Daniel > > > > > > > > i am inclined to say you are right and the fix is to fix the impl. > > > > > > Is there need for users to disable whatchdog at all? > > > It was always present since then and no one complained, > > > so perhaps we should ditch property instead fixing it > > > to keep it simple. > > > > Thinking about it more, I think we should NOT fix the 'enable_tco' property, > > because there will be no way for a mgmt appp to tell if they're using a > > fixed or broken QEMU. > > This is always the case for any bug. We don't as a rule add properties > for this, it is distro's responsibility to pick bugfixes for > features users care about. > > What makes this bug different? It is impossible to safely use the enable_tco property because it will break ABI across live migrations between old and new QEMU. If it was a recent bug I'd be ok with just fixing it. Since this property has been broken for 6 years though, IMHO it just needs to be deleted entirely. > > So if they use 'enable_tco' on a broken QEMU and then > > live migrate, they'll get an guest ABI change. If we did want to support > > disabling it, then we should have a brand new property that apps can probe > > for. > > > > In the absence of a request to disable watchdog, I'd say we just delete > > 'enable_tco' right now. If someone wants it in future, we can add it with > > a new name. > > I am really stressed about watchdog firing and resetting VMs that previously > were working fine. Adding this without a safety mechanism to quickly > disable in case of problems in the field is not wise imho. We would only toggle the ICH9-LPC.noreboot flag for new machine types, so wouldn't affect existing VMs, and if anyone has a problem they can explicitly set ICH9-LPC.noreboot back to true, or pick the older machine type again. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|