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Thu, 12 Jan 2023 20:38:45 +0000 (GMT) From: Matthew Rosato To: alex.williamson@redhat.com, pbonzini@redhat.com Cc: jgg@nvidia.com, cohuck@redhat.com, farman@linux.ibm.com, pmorel@linux.ibm.com, borntraeger@linux.ibm.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com, david@redhat.com, akrowiak@linux.ibm.com, jjherne@linux.ibm.com, pasic@linux.ibm.com, zhenyuw@linux.intel.com, zhi.a.wang@intel.com, seanjc@google.com, linux-s390@vger.kernel.org, kvm@vger.kernel.org, intel-gvt-dev@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] vfio: fix potential deadlock on vfio group lock Date: Thu, 12 Jan 2023 15:38:44 -0500 Message-Id: <20230112203844.41179-1-mjrosato@linux.ibm.com> X-Mailer: git-send-email 2.39.0 MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: U7gFq-EUrjV2Z9EY4ZwhqzpKbM3o8jrR X-Proofpoint-ORIG-GUID: R9uTHkQKN3zdwXH1Q6C-sB7bVKb_RBTZ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.923,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2023-01-12_12,2023-01-12_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 bulkscore=0 phishscore=0 adultscore=0 impostorscore=0 malwarescore=0 lowpriorityscore=0 spamscore=0 suspectscore=0 clxscore=1015 priorityscore=1501 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2301120146 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Currently it is possible that the final put of a KVM reference comes from vfio during its device close operation. This occurs while the vfio group lock is held; however, if the vfio device is still in the kvm device list, then the following call chain could result in a deadlock: kvm_put_kvm -> kvm_destroy_vm -> kvm_destroy_devices -> kvm_vfio_destroy -> kvm_vfio_file_set_kvm -> vfio_file_set_kvm -> group->group_lock/group_rwsem Avoid this scenario by having vfio core code acquire a KVM reference the first time a device is opened and hold that reference until the device fd is closed, at a point after the group lock has been released. Fixes: 421cfe6596f6 ("vfio: remove VFIO_GROUP_NOTIFY_SET_KVM") Reported-by: Alex Williamson Signed-off-by: Matthew Rosato --- Changes from v1: * Re-write using symbol get logic to get kvm ref during first device open, release the ref during device fd close after group lock is released * Drop kvm get/put changes to drivers; now that vfio core holds a kvm ref until sometime after the device_close op is called, it should be fine for drivers to get and put their own references to it. --- drivers/vfio/group.c | 6 ++--- drivers/vfio/vfio_main.c | 48 +++++++++++++++++++++++++++++++++++++--- include/linux/vfio.h | 1 - 3 files changed, 48 insertions(+), 7 deletions(-) diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c index bb24b2f0271e..2b0da82f82f4 100644 --- a/drivers/vfio/group.c +++ b/drivers/vfio/group.c @@ -165,9 +165,9 @@ static int vfio_device_group_open(struct vfio_device *device) } /* - * Here we pass the KVM pointer with the group under the lock. If the - * device driver will use it, it must obtain a reference and release it - * during close_device. + * Here we pass the KVM pointer with the group under the lock. A + * reference will be obtained the first time the device is opened and + * will be held until the device fd is closed. */ ret = vfio_device_open(device, device->group->iommufd, device->group->kvm); diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index 5177bb061b17..c969e2a0ecd3 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #include #include @@ -344,6 +345,35 @@ static bool vfio_assert_device_open(struct vfio_device *device) return !WARN_ON_ONCE(!READ_ONCE(device->open_count)); } +static bool vfio_kvm_get_kvm_safe(struct kvm *kvm) +{ + bool (*fn)(struct kvm *kvm); + bool ret; + + fn = symbol_get(kvm_get_kvm_safe); + if (WARN_ON(!fn)) + return false; + + ret = fn(kvm); + + symbol_put(kvm_get_kvm_safe); + + return ret; +} + +static void vfio_kvm_put_kvm(struct kvm *kvm) +{ + void (*fn)(struct kvm *kvm); + + fn = symbol_get(kvm_put_kvm); + if (WARN_ON(!fn)) + return; + + fn(kvm); + + symbol_put(kvm_put_kvm); +} + static int vfio_device_first_open(struct vfio_device *device, struct iommufd_ctx *iommufd, struct kvm *kvm) { @@ -361,16 +391,24 @@ static int vfio_device_first_open(struct vfio_device *device, if (ret) goto err_module_put; + if (kvm && !vfio_kvm_get_kvm_safe(kvm)) { + ret = -ENOENT; + goto err_unuse_iommu; + } device->kvm = kvm; if (device->ops->open_device) { ret = device->ops->open_device(device); if (ret) - goto err_unuse_iommu; + goto err_put_kvm; } return 0; +err_put_kvm: + if (kvm) { + vfio_kvm_put_kvm(kvm); + device->kvm = NULL; + } err_unuse_iommu: - device->kvm = NULL; if (iommufd) vfio_iommufd_unbind(device); else @@ -387,7 +425,6 @@ static void vfio_device_last_close(struct vfio_device *device, if (device->ops->close_device) device->ops->close_device(device); - device->kvm = NULL; if (iommufd) vfio_iommufd_unbind(device); else @@ -465,6 +502,11 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep) vfio_device_group_close(device); + if (device->open_count == 0 && device->kvm) { + vfio_kvm_put_kvm(device->kvm); + device->kvm = NULL; + } + vfio_device_put_registration(device); return 0; diff --git a/include/linux/vfio.h b/include/linux/vfio.h index 35be78e9ae57..3ff7e9302cc1 100644 --- a/include/linux/vfio.h +++ b/include/linux/vfio.h @@ -46,7 +46,6 @@ struct vfio_device { struct vfio_device_set *dev_set; struct list_head dev_set_list; unsigned int migration_flags; - /* Driver must reference the kvm during open_device or never touch it */ struct kvm *kvm; /* Members below here are private, not for driver use */