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Mon, 14 Nov 2022 16:01:52 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 458B4A4054; Mon, 14 Nov 2022 16:01:52 +0000 (GMT) Received: from pomme.tlslab.ibm.com (unknown [9.101.4.33]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 14 Nov 2022 16:01:52 +0000 (GMT) From: Laurent Dufour To: linuxppc-dev@lists.ozlabs.org Subject: [PATCH] powerpc/pseries: unregister VPA when hot unplugging a CPU Date: Mon, 14 Nov 2022 17:01:50 +0100 Message-Id: <20221114160150.13554-1-ldufour@linux.ibm.com> X-Mailer: git-send-email 2.38.1 MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: e0F07fp231BE45utOI5URh9bkp3UDv5C X-Proofpoint-GUID: w7Z9Beb4q_Pkzeyq52QoOjn3oC5GEK8L X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-11-14_12,2022-11-11_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 spamscore=0 malwarescore=0 adultscore=0 priorityscore=1501 bulkscore=0 phishscore=0 lowpriorityscore=0 clxscore=1015 suspectscore=0 mlxscore=0 mlxlogscore=809 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2210170000 definitions=main-2211140110 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Nathan Lynch , npiggin@gmail.com Errors-To: linuxppc-dev-bounces+incoming=patchwork.ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" The VPA should unregister when offlining a CPU. Otherwise there could be a short window where 2 CPUs could share the same VPA. This happens because the hypervisor is still keeping the VPA attached to the vCPU even if it became offline. Here is a potential situation: 1. remove proc A, 2. add proc B. If proc B gets proc A's place in cpu_present_map, then it registers proc A's VPAs. 3. If proc B is then re-added to the LP, its threads are sharing VPAs with proc A briefly as they come online. As the hypervisor may check for the VPA's yield_count field oddity, it may detects an unexpected value and kill the LPAR. Suggested-by: Nathan Lynch Signed-off-by: Laurent Dufour Reviewed-by: Nathan Lynch --- arch/powerpc/platforms/pseries/hotplug-cpu.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c index e0a7ac5db15d..090ae5a1e0f5 100644 --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c @@ -70,6 +70,7 @@ static void pseries_cpu_offline_self(void) xics_teardown_cpu(); unregister_slb_shadow(hwcpu); + unregister_vpa(hwcpu); rtas_stop_self(); /* Should never get here... */