| Message ID | 20230131200635.44227-1-mjrosato@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfio: fix deadlock between group lock and kvm lock | expand |
On Tue, Jan 31, 2023 at 03:06:35PM -0500, Matthew Rosato wrote: > @@ -799,13 +794,14 @@ EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent); > void vfio_file_set_kvm(struct file *file, struct kvm *kvm) > { > struct vfio_group *group = file->private_data; > + unsigned long flags; > > if (!vfio_file_is_group(file)) > return; > > - mutex_lock(&group->group_lock); > + spin_lock_irqsave(&group->kvm_ref_lock, flags); > group->kvm = kvm; > - mutex_unlock(&group->group_lock); > + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); We know we are in a sleeping context here so these are just 'spin_lock()', same with the other one Otherwise it seems Ok to me Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Jason
> From: Matthew Rosato <mjrosato@linux.ibm.com> > Sent: Wednesday, February 1, 2023 4:07 AM > > - device->kvm = kvm; > + /* > + * 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. Save the pointer in the device for use by > + * drivers. > + */ > + spin_lock_irqsave(&group->kvm_ref_lock, flags); > + if (group->kvm && vfio_kvm_get_kvm_safe(device, group->kvm)) > + device->kvm = group->kvm; > + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); > + No group reference in vfio_main.c. btw Yi, looks the deadlock issue also exists in your cdev work. kvm_vfio_release() holds kvm lock and then try to acquire device->device_set->lock in vfio_device_file_set_kvm(). vfio_device_ioctl_bind_iommufd() holds device->device_set->lock and then call vfio_device_open() which finally hit kvm lock acquisition in driver's open_device routine (e.g. vfio-ap). A similar fix is required in your series. Thanks Kevin
> From: Matthew Rosato <mjrosato@linux.ibm.com> > Sent: Wednesday, February 1, 2023 4:07 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> > --- > drivers/vfio/group.c | 14 +++---- > drivers/vfio/vfio.h | 5 ++- > drivers/vfio/vfio_main.c | 88 > ++++++++++++++++++++++++++++++++++++---- > include/linux/vfio.h | 2 +- > 4 files changed, 88 insertions(+), 21 deletions(-) > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > index bb24b2f0271e..8f67d33e0e8d 100644 > --- a/drivers/vfio/group.c > +++ b/drivers/vfio/group.c > @@ -164,13 +164,7 @@ static int vfio_device_group_open(struct > vfio_device *device) > goto out_unlock; > } > > - /* > - * 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. > - */ > - ret = vfio_device_open(device, device->group->iommufd, > - device->group->kvm); > + ret = vfio_device_open(device, device->group); > > out_unlock: > mutex_unlock(&device->group->group_lock); > @@ -450,6 +444,7 @@ 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; > @@ -799,13 +794,14 @@ > EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent); > void vfio_file_set_kvm(struct file *file, struct kvm *kvm) > { > struct vfio_group *group = file->private_data; > + unsigned long flags; > > if (!vfio_file_is_group(file)) > return; > > - mutex_lock(&group->group_lock); > + spin_lock_irqsave(&group->kvm_ref_lock, flags); > group->kvm = kvm; > - mutex_unlock(&group->group_lock); > + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); > } > EXPORT_SYMBOL_GPL(vfio_file_set_kvm); > > diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h > index f8219a438bfb..d153ad35de24 100644 > --- a/drivers/vfio/vfio.h > +++ b/drivers/vfio/vfio.h > @@ -15,11 +15,11 @@ struct iommufd_ctx; > struct iommu_group; > struct vfio_device; > struct vfio_container; > +struct vfio_group; > > void vfio_device_put_registration(struct vfio_device *device); > bool vfio_device_try_get_registration(struct vfio_device *device); > -int vfio_device_open(struct vfio_device *device, > - struct iommufd_ctx *iommufd, struct kvm *kvm); > +int vfio_device_open(struct vfio_device *device, struct vfio_group > *group); > void vfio_device_close(struct vfio_device *device, > struct iommufd_ctx *iommufd); > > @@ -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, > diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c > index 5177bb061b17..b0defb0d0d87 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> > @@ -344,9 +347,59 @@ static bool vfio_assert_device_open(struct > vfio_device *device) > return !WARN_ON_ONCE(!READ_ONCE(device->open_count)); > } > > +#ifdef CONFIG_HAVE_KVM > +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, struct kvm > *kvm) > +{ > + void (*pfn)(struct kvm *kvm); > + bool (*fn)(struct kvm *kvm); > + bool ret; > + > + pfn = symbol_get(kvm_put_kvm); > + if (WARN_ON(!pfn)) > + return false; > + > + fn = symbol_get(kvm_get_kvm_safe); > + if (WARN_ON(!fn)) { > + symbol_put(kvm_put_kvm); > + return false; > + } > + > + ret = fn(kvm); > + if (ret) > + device->put_kvm = pfn; > + else > + symbol_put(kvm_put_kvm); > + > + symbol_put(kvm_get_kvm_safe); > + > + return ret; > +} > + > +static void vfio_kvm_put_kvm(struct vfio_device *device) > +{ > + if (WARN_ON(!device->kvm || !device->put_kvm)) > + return; > + > + device->put_kvm(device->kvm); > + symbol_put(kvm_put_kvm); > +} > + > +#else > +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, struct kvm > *kvm) > +{ > + return false; > +} > + > +static void vfio_kvm_put_kvm(struct vfio_device *device) > +{ > +} > +#endif > + > static int vfio_device_first_open(struct vfio_device *device, > - struct iommufd_ctx *iommufd, struct kvm > *kvm) > + struct vfio_group *group) > { > + struct iommufd_ctx *iommufd = group->iommufd; > + unsigned long flags; > int ret; > > lockdep_assert_held(&device->dev_set->lock); > @@ -361,16 +414,30 @@ static int vfio_device_first_open(struct > vfio_device *device, > if (ret) > goto err_module_put; > > - device->kvm = kvm; > + /* > + * 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. Save the pointer in the device for use by > + * drivers. > + */ > + spin_lock_irqsave(&group->kvm_ref_lock, flags); > + if (group->kvm && vfio_kvm_get_kvm_safe(device, group->kvm)) > + device->kvm = group->kvm; > + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); > + > if (device->ops->open_device) { > ret = device->ops->open_device(device); > if (ret) > - goto err_unuse_iommu; > + goto err_put_kvm; > } > return 0; > > -err_unuse_iommu: > - device->kvm = NULL; > +err_put_kvm: > + if (device->kvm) { > + vfio_kvm_put_kvm(device); > + device->put_kvm = NULL; Can "device->put_kvm = NULL;" be part of vfio_kvm_put_kvm()? Regards, Yi Liu
> From: Jason Gunthorpe <jgg@nvidia.com> > Sent: Wednesday, February 1, 2023 4:26 AM > > On Tue, Jan 31, 2023 at 03:06:35PM -0500, Matthew Rosato wrote: > > @@ -799,13 +794,14 @@ > EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent); > > void vfio_file_set_kvm(struct file *file, struct kvm *kvm) > > { > > struct vfio_group *group = file->private_data; > > + unsigned long flags; > > > > if (!vfio_file_is_group(file)) > > return; > > > > - mutex_lock(&group->group_lock); > > + spin_lock_irqsave(&group->kvm_ref_lock, flags); > > group->kvm = kvm; > > - mutex_unlock(&group->group_lock); > > + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); > > We know we are in a sleeping context here so these are just > 'spin_lock()', same with the other one a dumb question. Why spinlock is required here?
On 2/1/23 1:13 AM, Tian, Kevin wrote: >> From: Matthew Rosato <mjrosato@linux.ibm.com> >> Sent: Wednesday, February 1, 2023 4:07 AM >> >> - device->kvm = kvm; >> + /* >> + * 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. Save the pointer in the device for use by >> + * drivers. >> + */ >> + spin_lock_irqsave(&group->kvm_ref_lock, flags); >> + if (group->kvm && vfio_kvm_get_kvm_safe(device, group->kvm)) >> + device->kvm = group->kvm; >> + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); >> + > > No group reference in vfio_main.c. OK -- I think to do that I'll have to move the lock/unlock of the dev_set lock to group.c right before we call vfio_device_{open,close} and check open_count there to make decisions about the kvm ref (before calling vfio_device_open to decide to get kvm ref, after returning from vfio_device_open to see if we to drop ref on error, after close to see if we need to drop ref). > > btw Yi, looks the deadlock issue also exists in your cdev work. > > kvm_vfio_release() holds kvm lock and then try to acquire > device->device_set->lock in vfio_device_file_set_kvm(). > > vfio_device_ioctl_bind_iommufd() holds device->device_set->lock > and then call vfio_device_open() which finally hit kvm lock > acquisition in driver's open_device routine (e.g. vfio-ap). > > A similar fix is required in your series. > > Thanks > Kevin
On 2/1/23 7:42 AM, Liu, Yi L wrote: >> From: Matthew Rosato <mjrosato@linux.ibm.com> ... >> + if (device->kvm) { >> + vfio_kvm_put_kvm(device); >> + device->put_kvm = NULL; > > Can "device->put_kvm = NULL;" be part of vfio_kvm_put_kvm()? Sure
On 2/1/23 7:43 AM, Liu, Yi L wrote: >> From: Jason Gunthorpe <jgg@nvidia.com> >> Sent: Wednesday, February 1, 2023 4:26 AM >> >> On Tue, Jan 31, 2023 at 03:06:35PM -0500, Matthew Rosato wrote: >>> @@ -799,13 +794,14 @@ >> EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent); >>> void vfio_file_set_kvm(struct file *file, struct kvm *kvm) >>> { >>> struct vfio_group *group = file->private_data; >>> + unsigned long flags; >>> >>> if (!vfio_file_is_group(file)) >>> return; >>> >>> - mutex_lock(&group->group_lock); >>> + spin_lock_irqsave(&group->kvm_ref_lock, flags); >>> group->kvm = kvm; >>> - mutex_unlock(&group->group_lock); >>> + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); >> >> We know we are in a sleeping context here so these are just >> 'spin_lock()', same with the other one > > a dumb question. Why spinlock is required here?
> From: Matthew Rosato <mjrosato@linux.ibm.com> > Sent: Wednesday, February 1, 2023 10:43 PM > > On 2/1/23 7:43 AM, Liu, Yi L wrote: > >> From: Jason Gunthorpe <jgg@nvidia.com> > >> Sent: Wednesday, February 1, 2023 4:26 AM > >> > >> On Tue, Jan 31, 2023 at 03:06:35PM -0500, Matthew Rosato wrote: > >>> @@ -799,13 +794,14 @@ > >> EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent); > >>> void vfio_file_set_kvm(struct file *file, struct kvm *kvm) > >>> { > >>> struct vfio_group *group = file->private_data; > >>> + unsigned long flags; > >>> > >>> if (!vfio_file_is_group(file)) > >>> return; > >>> > >>> - mutex_lock(&group->group_lock); > >>> + spin_lock_irqsave(&group->kvm_ref_lock, flags); > >>> group->kvm = kvm; > >>> - mutex_unlock(&group->group_lock); > >>> + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); > >> > >> We know we are in a sleeping context here so these are just > >> 'spin_lock()', same with the other one > > > > a dumb question. Why spinlock is required here?
diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c index bb24b2f0271e..8f67d33e0e8d 100644 --- a/drivers/vfio/group.c +++ b/drivers/vfio/group.c @@ -164,13 +164,7 @@ static int vfio_device_group_open(struct vfio_device *device) goto out_unlock; } - /* - * 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. - */ - ret = vfio_device_open(device, device->group->iommufd, - device->group->kvm); + ret = vfio_device_open(device, device->group); out_unlock: mutex_unlock(&device->group->group_lock); @@ -450,6 +444,7 @@ 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; @@ -799,13 +794,14 @@ EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent); void vfio_file_set_kvm(struct file *file, struct kvm *kvm) { struct vfio_group *group = file->private_data; + unsigned long flags; if (!vfio_file_is_group(file)) return; - mutex_lock(&group->group_lock); + spin_lock_irqsave(&group->kvm_ref_lock, flags); group->kvm = kvm; - mutex_unlock(&group->group_lock); + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); } EXPORT_SYMBOL_GPL(vfio_file_set_kvm); diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h index f8219a438bfb..d153ad35de24 100644 --- a/drivers/vfio/vfio.h +++ b/drivers/vfio/vfio.h @@ -15,11 +15,11 @@ struct iommufd_ctx; struct iommu_group; struct vfio_device; struct vfio_container; +struct vfio_group; void vfio_device_put_registration(struct vfio_device *device); bool vfio_device_try_get_registration(struct vfio_device *device); -int vfio_device_open(struct vfio_device *device, - struct iommufd_ctx *iommufd, struct kvm *kvm); +int vfio_device_open(struct vfio_device *device, struct vfio_group *group); void vfio_device_close(struct vfio_device *device, struct iommufd_ctx *iommufd); @@ -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, diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index 5177bb061b17..b0defb0d0d87 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> @@ -344,9 +347,59 @@ static bool vfio_assert_device_open(struct vfio_device *device) return !WARN_ON_ONCE(!READ_ONCE(device->open_count)); } +#ifdef CONFIG_HAVE_KVM +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, struct kvm *kvm) +{ + void (*pfn)(struct kvm *kvm); + bool (*fn)(struct kvm *kvm); + bool ret; + + pfn = symbol_get(kvm_put_kvm); + if (WARN_ON(!pfn)) + return false; + + fn = symbol_get(kvm_get_kvm_safe); + if (WARN_ON(!fn)) { + symbol_put(kvm_put_kvm); + return false; + } + + ret = fn(kvm); + if (ret) + device->put_kvm = pfn; + else + symbol_put(kvm_put_kvm); + + symbol_put(kvm_get_kvm_safe); + + return ret; +} + +static void vfio_kvm_put_kvm(struct vfio_device *device) +{ + if (WARN_ON(!device->kvm || !device->put_kvm)) + return; + + device->put_kvm(device->kvm); + symbol_put(kvm_put_kvm); +} + +#else +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, struct kvm *kvm) +{ + return false; +} + +static void vfio_kvm_put_kvm(struct vfio_device *device) +{ +} +#endif + static int vfio_device_first_open(struct vfio_device *device, - struct iommufd_ctx *iommufd, struct kvm *kvm) + struct vfio_group *group) { + struct iommufd_ctx *iommufd = group->iommufd; + unsigned long flags; int ret; lockdep_assert_held(&device->dev_set->lock); @@ -361,16 +414,30 @@ static int vfio_device_first_open(struct vfio_device *device, if (ret) goto err_module_put; - device->kvm = kvm; + /* + * 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. Save the pointer in the device for use by + * drivers. + */ + spin_lock_irqsave(&group->kvm_ref_lock, flags); + if (group->kvm && vfio_kvm_get_kvm_safe(device, group->kvm)) + device->kvm = group->kvm; + spin_unlock_irqrestore(&group->kvm_ref_lock, flags); + if (device->ops->open_device) { ret = device->ops->open_device(device); if (ret) - goto err_unuse_iommu; + goto err_put_kvm; } return 0; -err_unuse_iommu: - device->kvm = NULL; +err_put_kvm: + if (device->kvm) { + vfio_kvm_put_kvm(device); + device->put_kvm = NULL; + device->kvm = NULL; + } if (iommufd) vfio_iommufd_unbind(device); else @@ -387,7 +454,11 @@ static void vfio_device_last_close(struct vfio_device *device, if (device->ops->close_device) device->ops->close_device(device); - device->kvm = NULL; + if (device->kvm) { + vfio_kvm_put_kvm(device); + device->kvm = NULL; + device->put_kvm = NULL; + } if (iommufd) vfio_iommufd_unbind(device); else @@ -395,15 +466,14 @@ static void vfio_device_last_close(struct vfio_device *device, module_put(device->dev->driver->owner); } -int vfio_device_open(struct vfio_device *device, - struct iommufd_ctx *iommufd, struct kvm *kvm) +int vfio_device_open(struct vfio_device *device, struct vfio_group *group) { int ret = 0; mutex_lock(&device->dev_set->lock); device->open_count++; if (device->open_count == 1) { - ret = vfio_device_first_open(device, iommufd, kvm); + ret = vfio_device_first_open(device, group); if (ret) device->open_count--; } 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 | 14 +++---- drivers/vfio/vfio.h | 5 ++- drivers/vfio/vfio_main.c | 88 ++++++++++++++++++++++++++++++++++++---- include/linux/vfio.h | 2 +- 4 files changed, 88 insertions(+), 21 deletions(-)