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Thu, 2 Feb 2023 16:24:45 +0000 (GMT) From: Matthew Rosato To: alex.williamson@redhat.com, pbonzini@redhat.com, yi.l.liu@intel.com, jgg@nvidia.com Cc: 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, kevin.tian@intel.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 v3] vfio: fix deadlock between group lock and kvm lock Date: Thu, 2 Feb 2023 11:24:42 -0500 Message-Id: <20230202162442.78216-1-mjrosato@linux.ibm.com> X-Mailer: git-send-email 2.39.1 MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: NnuhXHeZbpwQwNNnUjIfoo7hXWVih8FY X-Proofpoint-GUID: 4i-hlKKCT3KD8sTol1scOd6mtmDRRsmK X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.930,Hydra:6.0.562,FMLib:17.11.122.1 definitions=2023-02-02_10,2023-02-02_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 clxscore=1015 suspectscore=0 adultscore=0 bulkscore=0 impostorscore=0 mlxscore=0 mlxlogscore=999 phishscore=0 spamscore=0 lowpriorityscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2302020143 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org After 51cdc8bc120e, we have another deadlock scenario between the kvm->lock and the vfio group_lock with two different codepaths acquiring the locks in different order. Specifically in vfio_open_device, vfio holds the vfio group_lock when issuing device->ops->open_device but some drivers (like vfio-ap) need to acquire kvm->lock during their open_device routine; Meanwhile, kvm_vfio_release will acquire the kvm->lock first before calling vfio_file_set_kvm which will acquire the vfio group_lock. To resolve this, let's remove the need for the vfio group_lock from the kvm_vfio_release codepath. This is done by introducing a new spinlock to protect modifications to the vfio group kvm pointer, and acquiring a kvm ref from within vfio while holding this spinlock, with the reference held until the last close for the device in question. Fixes: 51cdc8bc120e ("kvm/vfio: Fix potential deadlock on vfio group_lock") Reported-by: Anthony Krowiak Suggested-by: Jason Gunthorpe Signed-off-by: Matthew Rosato --- Changes from v2: * Relocate the new functions back to vfio_main and externalize to call from group (Kevin) since cdev will need this too * s/vfio_kvm_*_kvm/vfio_device_*_kvm/ and only pass device as input. Handle new kvm_ref_lock directly inside vfio_device_get_kvm (Alex) * Add assert_lockdep_held for dev_set lock (Alex) * Internalize error paths for vfio_device_get_kvm_safe and now return void - either device->kvm is set with a ref taken or is NULL (Alex) * Other flow suggestions to make the call path cleaner - Thanks! (Alex) * Can't pass group->kvm to vfio_device_open, as it references the value outside of new lock. Pass device->kvm to minimize changes in this fix (Alex, Yi) Changes from v1: * use spin_lock instead of spin_lock_irqsave (Jason) * clear device->kvm_put as part of vfio_kvm_put_kvm (Yi) * Re-arrange code to avoid referencing the group contents from within vfio_main (Kevin) which meant moving most of the code in this patch to group.c along with getting/dropping of the dev_set lock --- drivers/vfio/group.c | 32 ++++++++++++++---- drivers/vfio/vfio.h | 14 ++++++++ drivers/vfio/vfio_main.c | 70 ++++++++++++++++++++++++++++++++++++---- include/linux/vfio.h | 2 +- 4 files changed, 103 insertions(+), 15 deletions(-) diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c index bb24b2f0271e..7fed4233ca23 100644 --- a/drivers/vfio/group.c +++ b/drivers/vfio/group.c @@ -164,13 +164,23 @@ static int vfio_device_group_open(struct vfio_device *device) goto out_unlock; } + mutex_lock(&device->dev_set->lock); + /* - * 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. + * Before the first device open, get the KVM pointer currently + * associated with the group (if there is one) and obtain a reference + * now that will be held until the open_count reaches 0 again. Save + * the pointer in the device for use by drivers. */ - ret = vfio_device_open(device, device->group->iommufd, - device->group->kvm); + if (device->open_count == 0) + vfio_device_get_kvm_safe(device); + + ret = vfio_device_open(device, device->group->iommufd, device->kvm); + + if (device->open_count == 0) + vfio_device_put_kvm(device); + + mutex_unlock(&device->dev_set->lock); out_unlock: mutex_unlock(&device->group->group_lock); @@ -180,7 +190,14 @@ static int vfio_device_group_open(struct vfio_device *device) void vfio_device_group_close(struct vfio_device *device) { mutex_lock(&device->group->group_lock); + mutex_lock(&device->dev_set->lock); + vfio_device_close(device, device->group->iommufd); + + if (device->open_count == 0) + vfio_device_put_kvm(device); + + mutex_unlock(&device->dev_set->lock); mutex_unlock(&device->group->group_lock); } @@ -450,6 +467,7 @@ static struct vfio_group *vfio_group_alloc(struct iommu_group *iommu_group, refcount_set(&group->drivers, 1); mutex_init(&group->group_lock); + spin_lock_init(&group->kvm_ref_lock); INIT_LIST_HEAD(&group->device_list); mutex_init(&group->device_lock); group->iommu_group = iommu_group; @@ -803,9 +821,9 @@ void vfio_file_set_kvm(struct file *file, struct kvm *kvm) if (!vfio_file_is_group(file)) return; - mutex_lock(&group->group_lock); + spin_lock(&group->kvm_ref_lock); group->kvm = kvm; - mutex_unlock(&group->group_lock); + spin_unlock(&group->kvm_ref_lock); } EXPORT_SYMBOL_GPL(vfio_file_set_kvm); diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h index f8219a438bfb..20d715b0a3a8 100644 --- a/drivers/vfio/vfio.h +++ b/drivers/vfio/vfio.h @@ -74,6 +74,7 @@ struct vfio_group { struct file *opened_file; struct blocking_notifier_head notifier; struct iommufd_ctx *iommufd; + spinlock_t kvm_ref_lock; }; int vfio_device_set_group(struct vfio_device *device, @@ -251,4 +252,17 @@ extern bool vfio_noiommu __read_mostly; enum { vfio_noiommu = false }; #endif +#ifdef CONFIG_HAVE_KVM +void vfio_device_get_kvm_safe(struct vfio_device *device); +void vfio_device_put_kvm(struct vfio_device *device); +#else +static inline void vfio_device_get_kvm_safe(struct vfio_device *device) +{ +} + +static inline void vfio_device_put_kvm(struct vfio_device *device) +{ +} +#endif + #endif diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index 5177bb061b17..4762550e9f42 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -16,6 +16,9 @@ #include #include #include +#ifdef CONFIG_HAVE_KVM +#include +#endif #include #include #include @@ -338,6 +341,62 @@ void vfio_unregister_group_dev(struct vfio_device *device) } EXPORT_SYMBOL_GPL(vfio_unregister_group_dev); +#ifdef CONFIG_HAVE_KVM +void vfio_device_get_kvm_safe(struct vfio_device *device) +{ + void (*pfn)(struct kvm *kvm); + bool (*fn)(struct kvm *kvm); + bool ret; + + lockdep_assert_held(&device->dev_set->lock); + + spin_lock(&device->group->kvm_ref_lock); + if (!device->group->kvm) + goto unlock; + + pfn = symbol_get(kvm_put_kvm); + if (WARN_ON(!pfn)) + goto unlock; + + fn = symbol_get(kvm_get_kvm_safe); + if (WARN_ON(!fn)) { + symbol_put(kvm_put_kvm); + goto unlock; + } + + ret = fn(device->group->kvm); + symbol_put(kvm_get_kvm_safe); + if (!ret) { + symbol_put(kvm_put_kvm); + goto unlock; + } + + device->put_kvm = pfn; + device->kvm = device->group->kvm; + +unlock: + spin_unlock(&device->group->kvm_ref_lock); +} + +void vfio_device_put_kvm(struct vfio_device *device) +{ + lockdep_assert_held(&device->dev_set->lock); + + if (!device->kvm) + return; + + if (WARN_ON(!device->put_kvm)) + goto clear; + + device->put_kvm(device->kvm); + device->put_kvm = NULL; + symbol_put(kvm_put_kvm); + +clear: + device->kvm = NULL; +} +#endif + /* true if the vfio_device has open_device() called but not close_device() */ static bool vfio_assert_device_open(struct vfio_device *device) { @@ -361,7 +420,6 @@ static int vfio_device_first_open(struct vfio_device *device, if (ret) goto err_module_put; - device->kvm = kvm; if (device->ops->open_device) { ret = device->ops->open_device(device); if (ret) @@ -370,7 +428,6 @@ static int vfio_device_first_open(struct vfio_device *device, return 0; err_unuse_iommu: - device->kvm = NULL; if (iommufd) vfio_iommufd_unbind(device); else @@ -387,7 +444,6 @@ 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 @@ -400,14 +456,14 @@ int vfio_device_open(struct vfio_device *device, { int ret = 0; - mutex_lock(&device->dev_set->lock); + lockdep_assert_held(&device->dev_set->lock); + device->open_count++; if (device->open_count == 1) { ret = vfio_device_first_open(device, iommufd, kvm); if (ret) device->open_count--; } - mutex_unlock(&device->dev_set->lock); return ret; } @@ -415,12 +471,12 @@ int vfio_device_open(struct vfio_device *device, void vfio_device_close(struct vfio_device *device, struct iommufd_ctx *iommufd) { - mutex_lock(&device->dev_set->lock); + lockdep_assert_held(&device->dev_set->lock); + vfio_assert_device_open(device); if (device->open_count == 1) vfio_device_last_close(device, iommufd); device->open_count--; - mutex_unlock(&device->dev_set->lock); } /* diff --git a/include/linux/vfio.h b/include/linux/vfio.h index 35be78e9ae57..87ff862ff555 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 */ @@ -58,6 +57,7 @@ struct vfio_device { struct list_head group_next; struct list_head iommu_entry; struct iommufd_access *iommufd_access; + void (*put_kvm)(struct kvm *kvm); #if IS_ENABLED(CONFIG_IOMMUFD) struct iommufd_device *iommufd_device; struct iommufd_ctx *iommufd_ictx;