| Message ID | 20230203215027.151988-2-mjrosato@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfio: fix deadlock between group lock and kvm lock | expand |
> From: Matthew Rosato <mjrosato@linux.ibm.com> > Sent: Saturday, February 4, 2023 5:50 AM > To: alex.williamson@redhat.com; pbonzini@redhat.com; Liu, Yi L > > 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 <akrowiak@linux.ibm.com> > Suggested-by: Jason Gunthorpe <jgg@nvidia.com> > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com> > --- > drivers/vfio/group.c | 44 +++++++++++++++++++++++----- > drivers/vfio/vfio.h | 15 ++++++++++ > drivers/vfio/vfio_main.c | 63 > +++++++++++++++++++++++++++++++++++----- > include/linux/vfio.h | 2 +- > 4 files changed, 109 insertions(+), 15 deletions(-) > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > index bb24b2f0271e..98621ac082f0 100644 > --- a/drivers/vfio/group.c > +++ b/drivers/vfio/group.c > @@ -154,6 +154,18 @@ static int vfio_group_ioctl_set_container(struct > vfio_group *group, > return ret; > } > > +static void vfio_device_group_get_kvm_safe(struct vfio_device *device) > +{ > + spin_lock(&device->group->kvm_ref_lock); > + if (!device->group->kvm) > + goto unlock; > + > + _vfio_device_get_kvm_safe(device, device->group->kvm); > + > +unlock: > + spin_unlock(&device->group->kvm_ref_lock); > +} > + > static int vfio_device_group_open(struct vfio_device *device) > { > int ret; > @@ -164,13 +176,23 @@ 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 Nit: a redundant space before "Save". Other part looks good to me. Reviewed-by: Yi Liu <yi.l.liu@intel.com> Regards, Yi Liu > + * 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_group_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 +202,14 @@ 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 +479,7 @@ 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 +833,9 @@ 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..24d6cd285945 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 +252,18 @@ 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, struct kvm > *kvm); > +void vfio_device_put_kvm(struct vfio_device *device); > +#else > +static inline void _vfio_device_get_kvm_safe(struct vfio_device *device, > + struct kvm *kvm) > +{ > +} > + > +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..28c47cd6a6b5 100644 > --- a/drivers/vfio/vfio_main.c > +++ b/drivers/vfio/vfio_main.c > @@ -16,6 +16,9 @@ > #include <linux/fs.h> > #include <linux/idr.h> > #include <linux/iommu.h> > +#ifdef CONFIG_HAVE_KVM > +#include <linux/kvm_host.h> > +#endif > #include <linux/list.h> > #include <linux/miscdevice.h> > #include <linux/module.h> > @@ -338,6 +341,55 @@ 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, struct kvm > *kvm) > +{ > + void (*pfn)(struct kvm *kvm); > + bool (*fn)(struct kvm *kvm); > + bool ret; > + > + lockdep_assert_held(&device->dev_set->lock); > + > + pfn = symbol_get(kvm_put_kvm); > + if (WARN_ON(!pfn)) > + return; > + > + fn = symbol_get(kvm_get_kvm_safe); > + if (WARN_ON(!fn)) { > + symbol_put(kvm_put_kvm); > + return; > + } > + > + ret = fn(kvm); > + symbol_put(kvm_get_kvm_safe); > + if (!ret) { > + symbol_put(kvm_put_kvm); > + return; > + } > + > + device->put_kvm = pfn; > + device->kvm = kvm; > +} > + > +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 +413,6 @@ 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 +421,6 @@ 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 +437,6 @@ 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 +449,14 @@ 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 +464,12 @@ 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; > -- > 2.39.1
On Sat, 4 Feb 2023 06:21:48 +0000 "Liu, Yi L" <yi.l.liu@intel.com> wrote: > > From: Matthew Rosato <mjrosato@linux.ibm.com> > > Sent: Saturday, February 4, 2023 5:50 AM > > To: alex.williamson@redhat.com; pbonzini@redhat.com; Liu, Yi L > > > > 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 <akrowiak@linux.ibm.com> > > Suggested-by: Jason Gunthorpe <jgg@nvidia.com> > > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com> > > --- > > drivers/vfio/group.c | 44 +++++++++++++++++++++++----- > > drivers/vfio/vfio.h | 15 ++++++++++ > > drivers/vfio/vfio_main.c | 63 > > +++++++++++++++++++++++++++++++++++----- > > include/linux/vfio.h | 2 +- > > 4 files changed, 109 insertions(+), 15 deletions(-) > > > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > > index bb24b2f0271e..98621ac082f0 100644 > > --- a/drivers/vfio/group.c > > +++ b/drivers/vfio/group.c > > @@ -154,6 +154,18 @@ static int vfio_group_ioctl_set_container(struct > > vfio_group *group, > > return ret; > > } > > > > +static void vfio_device_group_get_kvm_safe(struct vfio_device *device) > > +{ > > + spin_lock(&device->group->kvm_ref_lock); > > + if (!device->group->kvm) > > + goto unlock; > > + > > + _vfio_device_get_kvm_safe(device, device->group->kvm); > > + > > +unlock: > > + spin_unlock(&device->group->kvm_ref_lock); > > +} > > + > > static int vfio_device_group_open(struct vfio_device *device) > > { > > int ret; > > @@ -164,13 +176,23 @@ 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 > > Nit: a redundant space before "Save". Other part looks good to me. Two spaces between sentences is a common standard. Not everyone prefers this, but I do. Thanks, Alex > Reviewed-by: Yi Liu <yi.l.liu@intel.com> > > Regards, > Yi Liu > > > + * 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_group_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 +202,14 @@ 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 +479,7 @@ 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 +833,9 @@ 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..24d6cd285945 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 +252,18 @@ 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, struct kvm > > *kvm); > > +void vfio_device_put_kvm(struct vfio_device *device); > > +#else > > +static inline void _vfio_device_get_kvm_safe(struct vfio_device *device, > > + struct kvm *kvm) > > +{ > > +} > > + > > +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..28c47cd6a6b5 100644 > > --- a/drivers/vfio/vfio_main.c > > +++ b/drivers/vfio/vfio_main.c > > @@ -16,6 +16,9 @@ > > #include <linux/fs.h> > > #include <linux/idr.h> > > #include <linux/iommu.h> > > +#ifdef CONFIG_HAVE_KVM > > +#include <linux/kvm_host.h> > > +#endif > > #include <linux/list.h> > > #include <linux/miscdevice.h> > > #include <linux/module.h> > > @@ -338,6 +341,55 @@ 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, struct kvm > > *kvm) > > +{ > > + void (*pfn)(struct kvm *kvm); > > + bool (*fn)(struct kvm *kvm); > > + bool ret; > > + > > + lockdep_assert_held(&device->dev_set->lock); > > + > > + pfn = symbol_get(kvm_put_kvm); > > + if (WARN_ON(!pfn)) > > + return; > > + > > + fn = symbol_get(kvm_get_kvm_safe); > > + if (WARN_ON(!fn)) { > > + symbol_put(kvm_put_kvm); > > + return; > > + } > > + > > + ret = fn(kvm); > > + symbol_put(kvm_get_kvm_safe); > > + if (!ret) { > > + symbol_put(kvm_put_kvm); > > + return; > > + } > > + > > + device->put_kvm = pfn; > > + device->kvm = kvm; > > +} > > + > > +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 +413,6 @@ 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 +421,6 @@ 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 +437,6 @@ 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 +449,14 @@ 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 +464,12 @@ 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; > > -- > > 2.39.1 >
> From: Matthew Rosato <mjrosato@linux.ibm.com> > Sent: Saturday, February 4, 2023 5:50 AM > > 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 <akrowiak@linux.ibm.com> > Suggested-by: Jason Gunthorpe <jgg@nvidia.com> > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Tony Krowiak <akrowiak@linux.ibm.com> On 2/3/23 4:50 PM, Matthew Rosato wrote: > 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 <akrowiak@linux.ibm.com> > Suggested-by: Jason Gunthorpe <jgg@nvidia.com> > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com> > --- > drivers/vfio/group.c | 44 +++++++++++++++++++++++----- > drivers/vfio/vfio.h | 15 ++++++++++ > drivers/vfio/vfio_main.c | 63 +++++++++++++++++++++++++++++++++++----- > include/linux/vfio.h | 2 +- > 4 files changed, 109 insertions(+), 15 deletions(-) > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > index bb24b2f0271e..98621ac082f0 100644 > --- a/drivers/vfio/group.c > +++ b/drivers/vfio/group.c > @@ -154,6 +154,18 @@ static int vfio_group_ioctl_set_container(struct vfio_group *group, > return ret; > } > > +static void vfio_device_group_get_kvm_safe(struct vfio_device *device) > +{ > + spin_lock(&device->group->kvm_ref_lock); > + if (!device->group->kvm) > + goto unlock; > + > + _vfio_device_get_kvm_safe(device, device->group->kvm); > + > +unlock: > + spin_unlock(&device->group->kvm_ref_lock); > +} > + > static int vfio_device_group_open(struct vfio_device *device) > { > int ret; > @@ -164,13 +176,23 @@ 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_group_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 +202,14 @@ 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 +479,7 @@ 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 +833,9 @@ 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..24d6cd285945 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 +252,18 @@ 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, struct kvm *kvm); > +void vfio_device_put_kvm(struct vfio_device *device); > +#else > +static inline void _vfio_device_get_kvm_safe(struct vfio_device *device, > + struct kvm *kvm) > +{ > +} > + > +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..28c47cd6a6b5 100644 > --- a/drivers/vfio/vfio_main.c > +++ b/drivers/vfio/vfio_main.c > @@ -16,6 +16,9 @@ > #include <linux/fs.h> > #include <linux/idr.h> > #include <linux/iommu.h> > +#ifdef CONFIG_HAVE_KVM > +#include <linux/kvm_host.h> > +#endif > #include <linux/list.h> > #include <linux/miscdevice.h> > #include <linux/module.h> > @@ -338,6 +341,55 @@ 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, struct kvm *kvm) > +{ > + void (*pfn)(struct kvm *kvm); > + bool (*fn)(struct kvm *kvm); > + bool ret; > + > + lockdep_assert_held(&device->dev_set->lock); > + > + pfn = symbol_get(kvm_put_kvm); > + if (WARN_ON(!pfn)) > + return; > + > + fn = symbol_get(kvm_get_kvm_safe); > + if (WARN_ON(!fn)) { > + symbol_put(kvm_put_kvm); > + return; > + } > + > + ret = fn(kvm); > + symbol_put(kvm_get_kvm_safe); > + if (!ret) { > + symbol_put(kvm_put_kvm); > + return; > + } > + > + device->put_kvm = pfn; > + device->kvm = kvm; > +} > + > +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 +413,6 @@ 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 +421,6 @@ 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 +437,6 @@ 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 +449,14 @@ 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 +464,12 @@ 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;
diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c index bb24b2f0271e..98621ac082f0 100644 --- a/drivers/vfio/group.c +++ b/drivers/vfio/group.c @@ -154,6 +154,18 @@ static int vfio_group_ioctl_set_container(struct vfio_group *group, return ret; } +static void vfio_device_group_get_kvm_safe(struct vfio_device *device) +{ + spin_lock(&device->group->kvm_ref_lock); + if (!device->group->kvm) + goto unlock; + + _vfio_device_get_kvm_safe(device, device->group->kvm); + +unlock: + spin_unlock(&device->group->kvm_ref_lock); +} + static int vfio_device_group_open(struct vfio_device *device) { int ret; @@ -164,13 +176,23 @@ 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_group_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 +202,14 @@ 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 +479,7 @@ 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 +833,9 @@ 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..24d6cd285945 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 +252,18 @@ 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, struct kvm *kvm); +void vfio_device_put_kvm(struct vfio_device *device); +#else +static inline void _vfio_device_get_kvm_safe(struct vfio_device *device, + struct kvm *kvm) +{ +} + +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..28c47cd6a6b5 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -16,6 +16,9 @@ #include <linux/fs.h> #include <linux/idr.h> #include <linux/iommu.h> +#ifdef CONFIG_HAVE_KVM +#include <linux/kvm_host.h> +#endif #include <linux/list.h> #include <linux/miscdevice.h> #include <linux/module.h> @@ -338,6 +341,55 @@ 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, struct kvm *kvm) +{ + void (*pfn)(struct kvm *kvm); + bool (*fn)(struct kvm *kvm); + bool ret; + + lockdep_assert_held(&device->dev_set->lock); + + pfn = symbol_get(kvm_put_kvm); + if (WARN_ON(!pfn)) + return; + + fn = symbol_get(kvm_get_kvm_safe); + if (WARN_ON(!fn)) { + symbol_put(kvm_put_kvm); + return; + } + + ret = fn(kvm); + symbol_put(kvm_get_kvm_safe); + if (!ret) { + symbol_put(kvm_put_kvm); + return; + } + + device->put_kvm = pfn; + device->kvm = kvm; +} + +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 +413,6 @@ 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 +421,6 @@ 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 +437,6 @@ 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 +449,14 @@ 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 +464,12 @@ 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;
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 <akrowiak@linux.ibm.com> Suggested-by: Jason Gunthorpe <jgg@nvidia.com> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com> --- drivers/vfio/group.c | 44 +++++++++++++++++++++++----- drivers/vfio/vfio.h | 15 ++++++++++ drivers/vfio/vfio_main.c | 63 +++++++++++++++++++++++++++++++++++----- include/linux/vfio.h | 2 +- 4 files changed, 109 insertions(+), 15 deletions(-)