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Mon, 4 Apr 2022 22:11:53 +0000 (GMT) Received: from localhost.localdomain.com (unknown [9.65.234.56]) by b03ledav004.gho.boulder.ibm.com (Postfix) with ESMTP; Mon, 4 Apr 2022 22:11:53 +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 v19 08/20] s390/vfio-ap: introduce new mutex to control access to the KVM pointer Date: Mon, 4 Apr 2022 18:10:27 -0400 Message-Id: <20220404221039.1272245-9-akrowiak@linux.ibm.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20220404221039.1272245-1-akrowiak@linux.ibm.com> References: <20220404221039.1272245-1-akrowiak@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: fPUp2ST58Xzgew448yH0IYsGTIkNPvyY X-Proofpoint-ORIG-GUID: 2iv715rQWlP4nseeEk3iJeQ3w6mf54Cm X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.850,Hydra:6.0.425,FMLib:17.11.64.514 definitions=2022-04-04_09,2022-03-31_01,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 adultscore=0 mlxlogscore=999 malwarescore=0 spamscore=0 impostorscore=0 bulkscore=0 phishscore=0 lowpriorityscore=0 clxscore=1015 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2204040123 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 --- 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 0a5acd151a9b..c258e5f7fdfc 100644 --- a/drivers/s390/crypto/vfio_ap_drv.c +++ b/drivers/s390/crypto/vfio_ap_drv.c @@ -161,6 +161,7 @@ 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 5262e02192a4..ec926f2f2930 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;