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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=ham 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 90378C433DB for ; Fri, 15 Jan 2021 17:24:22 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id BB5E82399A for ; Fri, 15 Jan 2021 17:24:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BB5E82399A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kaod.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:33990 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l0Spf-0005Ug-KI for qemu-devel@archiver.kernel.org; Fri, 15 Jan 2021 12:24:19 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:40408) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l0Snw-0004PJ-GJ; Fri, 15 Jan 2021 12:22:32 -0500 Received: from smtpout1.mo804.mail-out.ovh.net ([79.137.123.220]:48007) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l0Sns-0001Z5-TM; Fri, 15 Jan 2021 12:22:32 -0500 Received: from mxplan5.mail.ovh.net (unknown [10.108.20.48]) by mo804.mail-out.ovh.net (Postfix) with ESMTPS id D7FDF827D32D; Fri, 15 Jan 2021 18:22:17 +0100 (CET) Received: from kaod.org (37.59.142.96) by DAG8EX1.mxp5.local (172.16.2.71) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2044.4; Fri, 15 Jan 2021 18:22:17 +0100 Authentication-Results: garm.ovh; auth=pass (GARM-96R001f7debb62-5d6c-48ed-9fdf-04444cec998f, DCCBFB19B1A3BA1C031047B2F93F7C58B25CC811) smtp.auth=groug@kaod.org X-OVh-ClientIp: 82.253.208.248 Date: Fri, 15 Jan 2021 18:22:16 +0100 From: Greg Kurz To: Daniel Henrique Barboza Subject: Re: [PATCH v1 7/7] spapr.c: consider CPU core online state before allowing unplug Message-ID: <20210115182216.6dccadee@bahia.lan> In-Reply-To: <20210114180628.1675603-8-danielhb413@gmail.com> References: <20210114180628.1675603-1-danielhb413@gmail.com> <20210114180628.1675603-8-danielhb413@gmail.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Originating-IP: [37.59.142.96] X-ClientProxiedBy: DAG1EX1.mxp5.local (172.16.2.1) To DAG8EX1.mxp5.local (172.16.2.71) X-Ovh-Tracer-GUID: 3bd46b67-3850-4d96-8d0b-d3dc6841d592 X-Ovh-Tracer-Id: 14936469643058911651 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgeduledrtddvgdejhecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfqggfjpdevjffgvefmvefgnecuuegrihhlohhuthemucehtddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpeffhffvuffkjghfofggtgfgihesthhqredtredtjeenucfhrhhomhepifhrvghgucfmuhhriicuoehgrhhouhhgsehkrghougdrohhrgheqnecuggftrfgrthhtvghrnhepvedtkeetieejvdehfefguddttdekleeljedukeejleevgfffheekteeifeejvdefnecuffhomhgrihhnpehrvgguhhgrthdrtghomhenucfkpheptddrtddrtddrtddpfeejrdehledrudegvddrleeinecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmohguvgepshhmthhpqdhouhhtpdhhvghlohepmhigphhlrghnhedrmhgrihhlrdhovhhhrdhnvghtpdhinhgvtheptddrtddrtddrtddpmhgrihhlfhhrohhmpehgrhhouhhgsehkrghougdrohhrghdprhgtphhtthhopeiguhhmrgesrhgvughhrghtrdgtohhm Received-SPF: pass client-ip=79.137.123.220; envelope-from=groug@kaod.org; helo=smtpout1.mo804.mail-out.ovh.net X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Xujun Ma , qemu-ppc@nongnu.org, qemu-devel@nongnu.org, david@gibson.dropbear.id.au Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 14 Jan 2021 15:06:28 -0300 Daniel Henrique Barboza wrote: > The only restriction we have when unplugging CPUs is to forbid unplug of > the boot cpu core. spapr_core_unplug_possible() does not contemplate the I can't remember why this restriction was introduced in the first place... This should be investigated and documented if the limitation still stands. > possibility of some cores being offlined by the guest, meaning that we're > rolling the dice regarding on whether we're unplugging the last online > CPU core the guest has. >=20 Trying to unplug the last CPU is obviously something that deserves special care. LoPAPR is quite explicit on the outcome : this should terminate the partition. 13.7.4.1.1. Isolation of CPUs The isolation of a CPU, in all cases, is preceded by the stop-self RTAS function for all processor threads, and the OS insures that all the CPU=E2=80=99s threads are in the RTAS stopped state prior to isolating = the CPU. Isolation of a processor that is not stopped produces unpredictable results. The stopping of the last processor thread of a LPAR partition effectively kills the partition, and at that point, ownership of all partition resources reverts to the platform firmware. R1-13.7.4.1.1-1. For the LRDR option: Prior to issuing the RTAS set-indicator specifying isolate isolation-state of a CPU DR connector type, all the CPU threads must be in the RTAS stopped state. R1-13.7.4.1.1-2. For the LRDR option: Stopping of the last processor thread of a LPAR partition with the stop-self RTAS function, must kill the partition, with ownership of all partition resources reverting to the platform firmware. This is clearly not how things work today : linux doesn't call "stop-self" on the last vCPU and even if it did, QEMU doesn't terminate the VM. If there's a valid reason to not implement this PAPR behavior, I'd like it to be documented. > If we hit the jackpot, we're going to detach the core DRC and pulse the > hotplug IRQ, but the guest OS will refuse to release the CPU. Our > spapr_core_unplug() DRC release callback will never be called and the CPU > core object will keep existing in QEMU. No error message will be sent > to the user, but the CPU core wasn't unplugged from the guest. >=20 > If the guest OS onlines the CPU core again we won't be able to hotunplug = it > either. 'dmesg' inside the guest will report a failed attempt to offline = an > unknown CPU: >=20 > [ 923.003994] pseries-hotplug-cpu: Failed to offline CPU , rc: -16 >=20 > This is the result of stopping the DRC state transition in the middle in = the > first failed attempt. >=20 Yes, at this point only a machine reset can fix things up. Given this is linux's choice not to call "stop-self" as it should do, I'm n= ot super fan of hardcoding this logic in QEMU, unless there are really good reasons to do so. > We can avoid this, and potentially other bad things from happening, if we > avoid to attempt the unplug altogether in this scenario. Let's check for > the online/offline state of the CPU cores in the guest before allowing > the hotunplug, and forbid removing a CPU core if it's the last one online > in the guest. >=20 > Reported-by: Xujun Ma > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=3D1911414 > Signed-off-by: Daniel Henrique Barboza > --- > hw/ppc/spapr.c | 39 ++++++++++++++++++++++++++++++++++++++- > 1 file changed, 38 insertions(+), 1 deletion(-) >=20 > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c > index a2f01c21aa..d269dcd102 100644 > --- a/hw/ppc/spapr.c > +++ b/hw/ppc/spapr.c > @@ -3709,9 +3709,16 @@ static void spapr_core_unplug(HotplugHandler *hotp= lug_dev, DeviceState *dev) > static int spapr_core_unplug_possible(HotplugHandler *hotplug_dev, CPUCo= re *cc, > Error **errp) > { > + CPUArchId *core_slot; > + SpaprCpuCore *core; > + PowerPCCPU *cpu; > + CPUState *cs; > + bool last_cpu_online =3D true; > int index; > =20 > - if (!spapr_find_cpu_slot(MACHINE(hotplug_dev), cc->core_id, &index))= { > + core_slot =3D spapr_find_cpu_slot(MACHINE(hotplug_dev), cc->core_id, > + &index); > + if (!core_slot) { > error_setg(errp, "Unable to find CPU core with core-id: %d", > cc->core_id); > return -1; > @@ -3722,6 +3729,36 @@ static int spapr_core_unplug_possible(HotplugHandl= er *hotplug_dev, CPUCore *cc, > return -1; > } > =20 > + /* Allow for any non-boot CPU core to be unplugged if already offlin= e */ > + core =3D SPAPR_CPU_CORE(core_slot->cpu); > + cs =3D CPU(core->threads[0]); > + if (cs->halted) { > + return 0; > + } > + > + /* > + * Do not allow core unplug if it's the last core online. > + */ > + cpu =3D POWERPC_CPU(cs); > + CPU_FOREACH(cs) { > + PowerPCCPU *c =3D POWERPC_CPU(cs); > + > + if (c =3D=3D cpu) { > + continue; > + } > + > + if (!cs->halted) { > + last_cpu_online =3D false; > + break; > + } > + } > + > + if (last_cpu_online) { > + error_setg(errp, "Unable to unplug CPU core with core-id %d: it = is " > + "the only CPU core online in the guest", cc->core_id); > + return -1; > + } > + > return 0; > } > =20