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=-10.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=unavailable 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 E1C10C433C1 for ; Thu, 25 Mar 2021 20:32:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B704161A40 for ; Thu, 25 Mar 2021 20:32:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230322AbhCYUcY (ORCPT ); Thu, 25 Mar 2021 16:32:24 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:61916 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S229977AbhCYUcU (ORCPT ); Thu, 25 Mar 2021 16:32:20 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 12PK5MPi112725; Thu, 25 Mar 2021 16:32:18 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=date : from : to : cc : subject : message-id : in-reply-to : references : mime-version : content-type : content-transfer-encoding; s=pp1; bh=oEpHvDI3puLg+Vq05BFMSURNGiOqUaXOZOQzdNfRnn8=; b=VsjPK/h/a14XiyiZzBLZYZnGWylzon8Hh/Awb8F1M7OwOD9WKnmYH6Nc2Zp/f9g8u+TJ CFFFVQLuxJqZs7mupOr9BbYgmPIwZMa9U5l+FiXwHZadc2eDRPP557qYaXnnI8eW939c CbY/rVGxgKk5AfCaanpZ7cWWfygHvyesgUvySULy0qZ1cmIreV1WbHrFdQNOxHX5JurH h/fVlEeOFi5T4OdQtKw3YmA3z2hFfruTlp1Tub1PoGKeby7RjDYHhSDwqSvbcXj0J4ao /sD15n1E2acERF+wOA+J5S4fApwZalWfDp/iWKeLEIYsPW7xdff64NsRp3OqaLpAlLe5 nQ== Received: from pps.reinject (localhost [127.0.0.1]) by mx0b-001b2d01.pphosted.com with ESMTP id 37h18egr2m-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 25 Mar 2021 16:32:18 -0400 Received: from m0098414.ppops.net (m0098414.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.43/8.16.0.43) with SMTP id 12PK5jpV114396; Thu, 25 Mar 2021 16:32:17 -0400 Received: from ppma06ams.nl.ibm.com (66.31.33a9.ip4.static.sl-reverse.com [169.51.49.102]) by mx0b-001b2d01.pphosted.com with ESMTP id 37h18egr17-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 25 Mar 2021 16:32:17 -0400 Received: from pps.filterd (ppma06ams.nl.ibm.com [127.0.0.1]) by ppma06ams.nl.ibm.com (8.16.0.43/8.16.0.43) with SMTP id 12PKRdK4025569; Thu, 25 Mar 2021 20:32:15 GMT Received: from b06avi18626390.portsmouth.uk.ibm.com (b06avi18626390.portsmouth.uk.ibm.com [9.149.26.192]) by ppma06ams.nl.ibm.com with ESMTP id 37h15100pn-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 25 Mar 2021 20:32:15 +0000 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06avi18626390.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 12PKVsF835455354 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 25 Mar 2021 20:31:54 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E71EFA4053; Thu, 25 Mar 2021 20:32:12 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 306E2A4051; Thu, 25 Mar 2021 20:32:12 +0000 (GMT) Received: from li-e979b1cc-23ba-11b2-a85c-dfd230f6cf82 (unknown [9.171.84.230]) by d06av23.portsmouth.uk.ibm.com (Postfix) with SMTP; Thu, 25 Mar 2021 20:32:12 +0000 (GMT) Date: Thu, 25 Mar 2021 21:32:10 +0100 From: Halil Pasic To: Tony Krowiak Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org, borntraeger@de.ibm.com, cohuck@redhat.com, kwankhede@nvidia.com, pbonzini@redhat.com, alex.williamson@redhat.com, pasic@linux.vnet.ibm.com Subject: Re: [PATCH v5 1/1] s390/vfio-ap: fix circular lockdep when setting/clearing crypto masks Message-ID: <20210325213210.62cb11b9.pasic@linux.ibm.com> In-Reply-To: <20210325124640.23995-2-akrowiak@linux.ibm.com> References: <20210325124640.23995-1-akrowiak@linux.ibm.com> <20210325124640.23995-2-akrowiak@linux.ibm.com> Organization: IBM 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=US-ASCII Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 5qRJTkiymQM0dqZpHznUPt1kLU6qfsUH X-Proofpoint-GUID: QXXZp66eNcmEuopvnEsEfdxFpPwpWzli X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.761 definitions=2021-03-25_07:2021-03-25,2021-03-25 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 phishscore=0 mlxlogscore=999 priorityscore=1501 impostorscore=0 mlxscore=0 malwarescore=0 spamscore=0 lowpriorityscore=0 adultscore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2103250000 definitions=main-2103250146 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, 25 Mar 2021 08:46:40 -0400 Tony Krowiak wrote: > This patch fixes a lockdep splat introduced by commit f21916ec4826 > ("s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated"). > The lockdep splat only occurs when starting a Secure Execution guest. > Crypto virtualization (vfio_ap) is not yet supported for SE guests; > however, in order to avoid this problem when support becomes available, > this fix is being provided. > > The circular locking dependency was introduced when the setting of the > masks in the guest's APCB was executed while holding the matrix_dev->lock. > While the lock is definitely needed to protect the setting/unsetting of the > matrix_mdev->kvm pointer, it is not necessarily critical for setting the > masks; so, the matrix_dev->lock will be released while the masks are being > set or cleared. > > Keep in mind, however, that another process that takes the matrix_dev->lock > can get control while the masks in the guest's APCB are being set or > cleared as a result of the driver being notified that the KVM pointer > has been set or unset. This could result in invalid access to the > matrix_mdev->kvm pointer by the intervening process. To avoid this > scenario, two new fields are being added to the ap_matrix_mdev struct: > > struct ap_matrix_mdev { > ... > bool kvm_busy; > wait_queue_head_t wait_for_kvm; > ... > }; > > The functions that handle notification that the KVM pointer value has > been set or cleared will set the kvm_busy flag to true until they are done > processing at which time they will set it to false and wake up the tasks on > the matrix_mdev->wait_for_kvm wait queue. Functions that require > access to matrix_mdev->kvm will sleep on the wait queue until they are > awakened at which time they can safely access the matrix_mdev->kvm > field. > > Fixes: f21916ec4826 ("s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated") > Cc: stable@vger.kernel.org > Signed-off-by: Tony Krowiak Reviewed-by: Halil Pasic I intend to give a couple of work-days to others, and if nobody objects merge this. (I will wait till Tuesday.) I've tested it and it does silence the lockdep splat. Regards, Halil