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 lists1p.gnu.org (lists1p.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 7B666C44501 for ; Mon, 13 Jul 2026 13:58:04 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wjHAK-0001HR-1T; Mon, 13 Jul 2026 09:57:48 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wjHAD-0001H8-KR for qemu-devel@nongnu.org; Mon, 13 Jul 2026 09:57:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wjHAA-0005hJ-Ep for qemu-devel@nongnu.org; Mon, 13 Jul 2026 09:57:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1783951057; 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=vprLLMxMgkmFZoq3V9aPKpeT/lbh9F4mkQAmNb309qM=; b=cA4jxBYY5xSivW+8ln5Bx5zVh+2hb0sVRffV4v+2tnRA+6GDO57jTB+6hTv4kd5c7+gV6K UPCNakbykQEQypt7d1b8vv2ThUoKs/WK+i7AnpAGDWKecjWSX8Y/cli+Y/3DMRTfO1KuYf EwtGArt04fU08IqZrutiW+muNiQIduo= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-680-DWkiaYvDOEe2l8jlDnUVFw-1; Mon, 13 Jul 2026 09:57:33 -0400 X-MC-Unique: DWkiaYvDOEe2l8jlDnUVFw-1 X-Mimecast-MFC-AGG-ID: DWkiaYvDOEe2l8jlDnUVFw_1783951052 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 14C6319300F1; Mon, 13 Jul 2026 13:57:29 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.4]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 07E9C3000B4C; Mon, 13 Jul 2026 13:57:28 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 943A821E6920; Mon, 13 Jul 2026 15:57:25 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: Peter Maydell , QEMU Developers , Paolo Bonzini , Pedro Barbuda , Mohamed Mediouni , Nicholas Piggin , Harsh Prateek Bora , Cornelia Huck , Eric Farman , Matthew Rosato Subject: Re: what is qemu_system_guest_panicked() for? In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Mon, 13 Jul 2026 13:14:23 +0100") References: <87cxwrtgfd.fsf@pond.sub.org> <87se5ngln1.fsf@pond.sub.org> Date: Mon, 13 Jul 2026 15:57:25 +0200 Message-ID: <87bjcbf0vu.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: permerror client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, T_SPF_PERMERROR=0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development 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 Daniel P. Berrang=C3=A9 writes: > On Mon, Jul 13, 2026 at 01:43:46PM +0200, Markus Armbruster wrote: >> Daniel P. Berrang=C3=A9 writes: >>=20 >> > On Mon, Jul 13, 2026 at 10:57:58AM +0200, Markus Armbruster wrote: >> >> Daniel P. Berrang=C3=A9 writes: >> >>=20 >> >> > On Fri, Jul 10, 2026 at 05:02:53PM +0100, Peter Maydell wrote: >> >>=20 >> >> [...] >> >>=20 >> >> >> So I guess my question is, is it OK to mash these two categories of >> >> >> "we can't keep running the VM" together, or should we define a new >> >> >> one for the "unrecoverable guest error" case, or do we already have >> >> >> some better thing to do that I missed? >> >> > >> >> > IMHO we should NOT be abusing "panicked" for cases which are >> >> > not guest OS panics. >> >>=20 >> >> Point. >> >>=20 >> >> > Adding new QMP events is cheap and we should do so. >> >>=20 >> >> Changing the event sent on a certain situation is technically a >> >> compatibility break. Would it matter here? >> > >> > What wins "compat break" or "bug fix" ? A strict POV prevents almost >> > any bug fixes, if you want to remain bug-for-bug compatible with >> > old QEMU. >>=20 >> There is no hard and fast rule. >>=20 >> If a patch changes behavior, and no one is around to observe it, should >> we still treat it as compatibility break? The pragmatic answer is no. >>=20 >> It's of course hard to be sure about non-observation. The pragmatic >> answer to that is "we use the best available data, and where it is >> lacking, reasonably conservative guesses." >>=20 >> How likely is it that the fix breaks something else, and how painful >> could such breakage be? Again, hard to be sure, thus reasonably >> conservative guesses. >>=20 >> > With my "management app" hat on, I want QEMU to stop sending panic >> > events for things that are not panics, as that is triggering incorrect >> > actions / admin activities. ie on a panic, I'm going to take a guest >> > memory dump and try to analyse what is broken in the guest kernel. >> > >> > The QAPI spec says: >> > >> > ## >> > # @GUEST_PANICKED: >> > # >> > # Emitted when guest OS panic is detected >> > >> > >> > and >> > >> > ## >> > # @RunState: >> > # >> > # An enumeration of VM run states. >> > # >> > .. >> > # @guest-panicked: guest has been panicked as a result of guest OS >> > # panic >> > >> > >> > I don't think "machine check exception" or "unknown VM exit" >> > can be said to match either of those docs, and thus fixing >> > compliance should trump bug-for-bug compatibility IMHO. >>=20 >> I'm not objecting, I just want the compatibility issues considered. >>=20 >> What are the known observers of GUEST_PANICKED? How would they be >> affected by the change? >>=20 >> What are the use cases for observing GUEST_PANICKED? How could they be >> affected? >>=20 >> Reasonably conservative guesses will do. > > When libvirt see a GUEST_PANICKED, it will transition the state to > "CRASHED" and assign a reason of "PANICKED" as the trigger / cause. > > Then depending on the guest XML config for it will do one > of > > * Take a core dump of QEMU > * Terminate QEMU > * Restart QEMU > * Take a core dump of QEMU and restart > * Leave it in crashed state (to allow a debugger to attach) > > > The "machine check" and "unknown VM exit" scenarios, would still map > to libvirt's "CRASHED" state, but we would want to assign distinct > "cause" for each of them. Say we add event GUEST_MACHINE_CHECK, then send it instead of GUEST_PANICKED on a machine check. With an updated version of libvirt, this changes exactly the "cause" recorded for a machine check in the "CRASHED" state. This change is desirable. Older versions of libvirt ignore the unknown GUEST_MACHINE_CHECK event. They therefore no longer take the action. This is undesirable, I'm afraid. Is it? An orderly transition could look like this: 1. Add a new event for each distinct cause, and emit the appropriate event in addition to GUEST_PANICKED. 2. Deprecate GUEST_PANICKED. 3. Remove GUEST_PANICKED after a suitable grace period.