From patchwork Tue Jun 21 15:51:22 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Anthony Krowiak X-Patchwork-Id: 12889442 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 514BCC433EF for ; Tue, 21 Jun 2022 15:52:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353260AbiFUPwE (ORCPT ); Tue, 21 Jun 2022 11:52:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33934 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353206AbiFUPvy (ORCPT ); Tue, 21 Jun 2022 11:51:54 -0400 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 510C82D1D7; Tue, 21 Jun 2022 08:51:49 -0700 (PDT) Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.17.1.5/8.17.1.5) with ESMTP id 25LFg7q3017028; 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Tue, 21 Jun 2022 15:51:44 +0000 (GMT) Received: from li-fed795cc-2ab6-11b2-a85c-f0946e4a8dff.ibm.com.com (unknown [9.160.18.227]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP; Tue, 21 Jun 2022 15:51:44 +0000 (GMT) From: Tony Krowiak To: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: jjherne@linux.ibm.com, freude@linux.ibm.com, borntraeger@de.ibm.com, cohuck@redhat.com, mjrosato@linux.ibm.com, pasic@linux.ibm.com, alex.williamson@redhat.com, kwankhede@nvidia.com, fiuczy@linux.ibm.com Subject: [PATCH v20 08/20] s390/vfio-ap: introduce new mutex to control access to the KVM pointer Date: Tue, 21 Jun 2022 11:51:22 -0400 Message-Id: <20220621155134.1932383-9-akrowiak@linux.ibm.com> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20220621155134.1932383-1-akrowiak@linux.ibm.com> References: <20220621155134.1932383-1-akrowiak@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: ZUdcupa91zMhnyHrBCQ8XQgs0i3gCJwi X-Proofpoint-ORIG-GUID: my7gpmwJH8MU2XX4jHWzh7j12XF7AX4g X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.883,Hydra:6.0.517,FMLib:17.11.64.514 definitions=2022-06-21_08,2022-06-21_01,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 phishscore=0 impostorscore=0 mlxscore=0 bulkscore=0 suspectscore=0 spamscore=0 adultscore=0 lowpriorityscore=0 priorityscore=1501 malwarescore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2204290000 definitions=main-2206210066 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org The vfio_ap device driver registers for notification when the pointer to the KVM object for a guest is set. Recall that the KVM lock (kvm->lock) mutex must be taken outside of the matrix_dev->lock mutex to prevent the reporting by lockdep of a circular locking dependency (a.k.a., a lockdep splat): * see commit 0cc00c8d4050 ("Fix circular lockdep when setting/clearing crypto masks") * see commit 86956e70761b ("replace open coded locks for VFIO_GROUP_NOTIFY_SET_KVM notification") With the introduction of support for hot plugging/unplugging AP devices passed through to a KVM guest, a new guests_lock mutex is introduced to ensure the proper locking order is maintained: struct ap_matrix_dev { ... struct mutex guests_lock; ... } The matrix_dev->guests_lock controls access to the matrix_mdev instances that hold the state for AP devices that have been passed through to a KVM guest. This lock must be held to control access to the KVM pointer (matrix_mdev->kvm) while the vfio_ap device driver is using it to plug/unplug AP devices passed through to the KVM guest. Keep in mind, the proper locking order must be maintained whenever dynamically updating a KVM guest's APCB to plug/unplug adapters, domains and control domains: 1. matrix_dev->guests_lock: required to use the KVM pointer - stored in a struct ap_matrix_mdev instance - to update a KVM guest's APCB 2. matrix_mdev->kvm->lock: required to update a guest's APCB 3. matrix_dev->mdevs_lock: required to access data stored in a struct ap_matrix_mdev instance. Signed-off-by: Tony Krowiak Reviewed-by: Jason J. Herne --- drivers/s390/crypto/vfio_ap_drv.c | 1 + drivers/s390/crypto/vfio_ap_private.h | 6 ++++++ 2 files changed, 7 insertions(+) diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c index ed162732b139..db8ca7bb3696 100644 --- a/drivers/s390/crypto/vfio_ap_drv.c +++ b/drivers/s390/crypto/vfio_ap_drv.c @@ -100,6 +100,7 @@ static int vfio_ap_matrix_dev_create(void) mutex_init(&matrix_dev->mdevs_lock); INIT_LIST_HEAD(&matrix_dev->mdev_list); + mutex_init(&matrix_dev->guests_lock); dev_set_name(&matrix_dev->device, "%s", VFIO_AP_DEV_NAME); matrix_dev->device.parent = root_device; diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h index 22278d85a801..82ac74e83e13 100644 --- a/drivers/s390/crypto/vfio_ap_private.h +++ b/drivers/s390/crypto/vfio_ap_private.h @@ -39,6 +39,11 @@ * single ap_matrix_mdev device. It's quite coarse but we don't * expect much contention. * @vfio_ap_drv: the vfio_ap device driver + * @guests_lock: mutex for controlling access to a guest that is using AP + * devices passed through by the vfio_ap device driver. This lock + * will be taken when the AP devices are plugged into or unplugged + * from a guest, and when an ap_matrix_mdev device is added to or + * removed from @mdev_list or the list is iterated. */ struct ap_matrix_dev { struct device device; @@ -47,6 +52,7 @@ struct ap_matrix_dev { struct list_head mdev_list; struct mutex mdevs_lock; struct ap_driver *vfio_ap_drv; + struct mutex guests_lock; }; extern struct ap_matrix_dev *matrix_dev;