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Tsirkin" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= 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: <20221110112700-mutt-send-email-mst@kernel.org> References: <20221031131934.425448-1-berrange@redhat.com> <20221031114835-mutt-send-email-mst@kernel.org> <20221101135724.7f89868c@fedora> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org 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? > 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. > > With regards, > Daniel 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. > -- > |: 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 :|