| Message ID | 20230201192010.42748-1-mjrosato@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] vfio: fix deadlock between group lock and kvm lock | expand |
On Wed, 1 Feb 2023 14:20:10 -0500 Matthew Rosato <mjrosato@linux.ibm.com> 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> > --- > 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 | 90 +++++++++++++++++++++++++++++++++++++--- > drivers/vfio/vfio.h | 1 + > drivers/vfio/vfio_main.c | 11 ++--- > include/linux/vfio.h | 2 +- > 4 files changed, 91 insertions(+), 13 deletions(-) > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > index bb24b2f0271e..52f434861294 100644 > --- a/drivers/vfio/group.c > +++ b/drivers/vfio/group.c > @@ -13,6 +13,9 @@ > #include <linux/vfio.h> > #include <linux/iommufd.h> > #include <linux/anon_inodes.h> > +#ifdef CONFIG_HAVE_KVM > +#include <linux/kvm_host.h> > +#endif > #include "vfio.h" > > static struct vfio { > @@ -154,6 +157,55 @@ static int vfio_group_ioctl_set_container(struct vfio_group *group, > return ret; > } > > +#ifdef CONFIG_HAVE_KVM > +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, struct kvm *kvm) I'm tempted to name these vfio_device_get_kvm_safe() and only pass the vfio_device, where of course we can get the kvm pointer from the group internally. > +{ > + void (*pfn)(struct kvm *kvm); > + bool (*fn)(struct kvm *kvm); > + bool ret; > + We should assert_lockdep_held(&device->dev_set->lock) in both of these since that seems to be what's protecting device->kvm and device->put_kvm. If we change as above to get the kvm pointer from the group within this function, we can also move the kvm_ref_lock here, which seems to simplify the caller quite a bit. > + 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; It simplifies the caller if we can use this even in the !device->kvm case. > + > + device->put_kvm(device->kvm); > + device->put_kvm = NULL; > + 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_group_open(struct vfio_device *device) > { > int ret; > @@ -164,14 +216,32 @@ 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. > */ > + if (device->open_count == 0) { > + spin_lock(&device->group->kvm_ref_lock); > + if (device->group->kvm && > + vfio_kvm_get_kvm_safe(device, device->group->kvm)) > + device->kvm = device->group->kvm; > + spin_unlock(&device->group->kvm_ref_lock); > + } > + > ret = vfio_device_open(device, device->group->iommufd, > device->group->kvm); We're using device->group->kvm outside of kvm_ref_lock here, it should be using device->kvm. > > + if (ret && device->kvm && device->open_count == 0) { Slightly redundant, if device->open_count == 0 here, we can infer ret is non-zero. I fiddled with it a little further, see if you like anything from the version below and incorporate what you do. Thanks, Alex diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c index bb24b2f0271e..5121a34e1489 100644 --- a/drivers/vfio/group.c +++ b/drivers/vfio/group.c @@ -13,6 +13,9 @@ #include <linux/vfio.h> #include <linux/iommufd.h> #include <linux/anon_inodes.h> +#ifdef CONFIG_HAVE_KVM +#include <linux/kvm_host.h> +#endif #include "vfio.h" static struct vfio { @@ -154,6 +157,64 @@ static int vfio_group_ioctl_set_container(struct vfio_group *group, return ret; } +#ifdef CONFIG_HAVE_KVM +static 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); +} + +static 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; +} +#else +static void vfio_device_get_kvm_safe(struct vfio_device *device) {} +static void vfio_device_put_kvm(struct vfio_device *device) {} +#endif + static int vfio_device_group_open(struct vfio_device *device) { int ret; @@ -164,13 +225,23 @@ 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 +251,14 @@ 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 +528,7 @@ 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 +882,9 @@ 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..20c6bc249cb8 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, diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index 5177bb061b17..14dbf781ea8c 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -361,7 +361,6 @@ 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 +369,6 @@ 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 +385,6 @@ 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 +397,14 @@ 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 +412,12 @@ 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;
> From: Alex Williamson <alex.williamson@redhat.com> > Sent: Thursday, February 2, 2023 7:28 AM > > On Wed, 1 Feb 2023 14:20:10 -0500 > Matthew Rosato <mjrosato@linux.ibm.com> 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> > > --- > > 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 | 90 > +++++++++++++++++++++++++++++++++++++--- > > drivers/vfio/vfio.h | 1 + > > drivers/vfio/vfio_main.c | 11 ++--- > > include/linux/vfio.h | 2 +- > > 4 files changed, 91 insertions(+), 13 deletions(-) > > > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > > index bb24b2f0271e..52f434861294 100644 > > --- a/drivers/vfio/group.c > > +++ b/drivers/vfio/group.c > > @@ -13,6 +13,9 @@ > > #include <linux/vfio.h> > > #include <linux/iommufd.h> > > #include <linux/anon_inodes.h> > > +#ifdef CONFIG_HAVE_KVM > > +#include <linux/kvm_host.h> > > +#endif > > #include "vfio.h" > > > > static struct vfio { > > @@ -154,6 +157,55 @@ static int vfio_group_ioctl_set_container(struct > vfio_group *group, > > return ret; > > } > > > > +#ifdef CONFIG_HAVE_KVM > > +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, struct > kvm *kvm) > > I'm tempted to name these vfio_device_get_kvm_safe() and only pass the > vfio_device, where of course we can get the kvm pointer from the group > internally. > > > +{ > > + void (*pfn)(struct kvm *kvm); > > + bool (*fn)(struct kvm *kvm); > > + bool ret; > > + > > We should assert_lockdep_held(&device->dev_set->lock) in both of these > since that seems to be what's protecting device->kvm and > device->put_kvm. > > If we change as above to get the kvm pointer from the group within this > function, we can also move the kvm_ref_lock here, which seems to > simplify the caller quite a bit. > > > + 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; > > It simplifies the caller if we can use this even in the !device->kvm > case. > > > + > > + device->put_kvm(device->kvm); > > + device->put_kvm = NULL; > > + 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_group_open(struct vfio_device *device) > > { > > int ret; > > @@ -164,14 +216,32 @@ 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. > > */ > > + if (device->open_count == 0) { > > + spin_lock(&device->group->kvm_ref_lock); > > + if (device->group->kvm && > > + vfio_kvm_get_kvm_safe(device, device->group->kvm)) > > + device->kvm = device->group->kvm; > > + spin_unlock(&device->group->kvm_ref_lock); > > + } > > + > > ret = vfio_device_open(device, device->group->iommufd, > > device->group->kvm); > > We're using device->group->kvm outside of kvm_ref_lock here, it should > be using device->kvm. Existing code set device->kvm in the vfio_device_first_open() which is called by vfio_device_open(). After above change, seems not necessary to pass kvm pointer into the call chain. Isn't it? Regards, Yi Liu
> From: Liu, Yi L <yi.l.liu@intel.com> > Sent: Thursday, February 2, 2023 11:47 AM > > > ret = vfio_device_open(device, device->group->iommufd, > > > device->group->kvm); > > > > We're using device->group->kvm outside of kvm_ref_lock here, it should > > be using device->kvm. > > Existing code set device->kvm in the vfio_device_first_open() which is > called by vfio_device_open(). After above change, seems not necessary > to pass kvm pointer into the call chain. Isn't it? > Looks so.
> From: Alex Williamson <alex.williamson@redhat.com> > Sent: Thursday, February 2, 2023 7:28 AM > > > > +#ifdef CONFIG_HAVE_KVM > > +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, struct kvm > *kvm) > > I'm tempted to name these vfio_device_get_kvm_safe() and only pass the > vfio_device, where of course we can get the kvm pointer from the group > internally. > I have a different thought. In the end the cdev series also need the similar safe get/put logic then it's better to keep it in vfio_main.c called by the group/cdev path individually.
On Thu, 2 Feb 2023 03:46:59 +0000 "Liu, Yi L" <yi.l.liu@intel.com> wrote: > > From: Alex Williamson <alex.williamson@redhat.com> > > Sent: Thursday, February 2, 2023 7:28 AM > > > > On Wed, 1 Feb 2023 14:20:10 -0500 > > Matthew Rosato <mjrosato@linux.ibm.com> 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> > > > --- > > > 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 | 90 > > +++++++++++++++++++++++++++++++++++++--- > > > drivers/vfio/vfio.h | 1 + > > > drivers/vfio/vfio_main.c | 11 ++--- > > > include/linux/vfio.h | 2 +- > > > 4 files changed, 91 insertions(+), 13 deletions(-) > > > > > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > > > index bb24b2f0271e..52f434861294 100644 > > > --- a/drivers/vfio/group.c > > > +++ b/drivers/vfio/group.c > > > @@ -13,6 +13,9 @@ > > > #include <linux/vfio.h> > > > #include <linux/iommufd.h> > > > #include <linux/anon_inodes.h> > > > +#ifdef CONFIG_HAVE_KVM > > > +#include <linux/kvm_host.h> > > > +#endif > > > #include "vfio.h" > > > > > > static struct vfio { > > > @@ -154,6 +157,55 @@ static int vfio_group_ioctl_set_container(struct > > vfio_group *group, > > > return ret; > > > } > > > > > > +#ifdef CONFIG_HAVE_KVM > > > +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, struct > > kvm *kvm) > > > > I'm tempted to name these vfio_device_get_kvm_safe() and only pass the > > vfio_device, where of course we can get the kvm pointer from the group > > internally. > > > > > +{ > > > + void (*pfn)(struct kvm *kvm); > > > + bool (*fn)(struct kvm *kvm); > > > + bool ret; > > > + > > > > We should assert_lockdep_held(&device->dev_set->lock) in both of these > > since that seems to be what's protecting device->kvm and > > device->put_kvm. > > > > If we change as above to get the kvm pointer from the group within this > > function, we can also move the kvm_ref_lock here, which seems to > > simplify the caller quite a bit. > > > > > + 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; > > > > It simplifies the caller if we can use this even in the !device->kvm > > case. > > > > > + > > > + device->put_kvm(device->kvm); > > > + device->put_kvm = NULL; > > > + 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_group_open(struct vfio_device *device) > > > { > > > int ret; > > > @@ -164,14 +216,32 @@ 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. > > > */ > > > + if (device->open_count == 0) { > > > + spin_lock(&device->group->kvm_ref_lock); > > > + if (device->group->kvm && > > > + vfio_kvm_get_kvm_safe(device, device->group->kvm)) > > > + device->kvm = device->group->kvm; > > > + spin_unlock(&device->group->kvm_ref_lock); > > > + } > > > + > > > ret = vfio_device_open(device, device->group->iommufd, > > > device->group->kvm); > > > > We're using device->group->kvm outside of kvm_ref_lock here, it should > > be using device->kvm. > > Existing code set device->kvm in the vfio_device_first_open() which is > called by vfio_device_open(). After above change, seems not necessary > to pass kvm pointer into the call chain. Isn't it? Yes, we can get it from the device. I didn't check how much this bloats the patch though. As a fix, it might make sense to save that refactoring for a follow-on patch. Thanks, Alex
> -----Original Message----- > From: Alex Williamson <alex.williamson@redhat.com> > Sent: Thursday, February 2, 2023 12:15 PM > To: Liu, Yi L <yi.l.liu@intel.com> > Cc: Matthew Rosato <mjrosato@linux.ibm.com>; pbonzini@redhat.com; > 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; Wang, Zhi A <zhi.a.wang@intel.com>; > Christopherson,, Sean <seanjc@google.com>; Tian, Kevin > <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: Re: [PATCH v2] vfio: fix deadlock between group lock and kvm lock > > On Thu, 2 Feb 2023 03:46:59 +0000 > "Liu, Yi L" <yi.l.liu@intel.com> wrote: > > > > From: Alex Williamson <alex.williamson@redhat.com> > > > Sent: Thursday, February 2, 2023 7:28 AM > > > > > > On Wed, 1 Feb 2023 14:20:10 -0500 > > > Matthew Rosato <mjrosato@linux.ibm.com> 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> > > > > --- > > > > 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 | 90 > > > +++++++++++++++++++++++++++++++++++++--- > > > > drivers/vfio/vfio.h | 1 + > > > > drivers/vfio/vfio_main.c | 11 ++--- > > > > include/linux/vfio.h | 2 +- > > > > 4 files changed, 91 insertions(+), 13 deletions(-) > > > > > > > > diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c > > > > index bb24b2f0271e..52f434861294 100644 > > > > --- a/drivers/vfio/group.c > > > > +++ b/drivers/vfio/group.c > > > > @@ -13,6 +13,9 @@ > > > > #include <linux/vfio.h> > > > > #include <linux/iommufd.h> > > > > #include <linux/anon_inodes.h> > > > > +#ifdef CONFIG_HAVE_KVM > > > > +#include <linux/kvm_host.h> > > > > +#endif > > > > #include "vfio.h" > > > > > > > > static struct vfio { > > > > @@ -154,6 +157,55 @@ static int > vfio_group_ioctl_set_container(struct > > > vfio_group *group, > > > > return ret; > > > > } > > > > > > > > +#ifdef CONFIG_HAVE_KVM > > > > +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, > struct > > > kvm *kvm) > > > > > > I'm tempted to name these vfio_device_get_kvm_safe() and only pass > the > > > vfio_device, where of course we can get the kvm pointer from the > group > > > internally. > > > > > > > +{ > > > > + void (*pfn)(struct kvm *kvm); > > > > + bool (*fn)(struct kvm *kvm); > > > > + bool ret; > > > > + > > > > > > We should assert_lockdep_held(&device->dev_set->lock) in both of > these > > > since that seems to be what's protecting device->kvm and > > > device->put_kvm. > > > > > > If we change as above to get the kvm pointer from the group within this > > > function, we can also move the kvm_ref_lock here, which seems to > > > simplify the caller quite a bit. > > > > > > > + 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; > > > > > > It simplifies the caller if we can use this even in the !device->kvm > > > case. > > > > > > > + > > > > + device->put_kvm(device->kvm); > > > > + device->put_kvm = NULL; > > > > + 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_group_open(struct vfio_device *device) > > > > { > > > > int ret; > > > > @@ -164,14 +216,32 @@ 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. > > > > */ > > > > + if (device->open_count == 0) { > > > > + spin_lock(&device->group->kvm_ref_lock); > > > > + if (device->group->kvm && > > > > + vfio_kvm_get_kvm_safe(device, device->group->kvm)) > > > > + device->kvm = device->group->kvm; > > > > + spin_unlock(&device->group->kvm_ref_lock); > > > > + } > > > > + > > > > ret = vfio_device_open(device, device->group->iommufd, > > > > device->group->kvm); > > > > > > We're using device->group->kvm outside of kvm_ref_lock here, it > should > > > be using device->kvm. > > > > Existing code set device->kvm in the vfio_device_first_open() which is > > called by vfio_device_open(). After above change, seems not necessary > > to pass kvm pointer into the call chain. Isn't it? > > Yes, we can get it from the device. I didn't check how much this > bloats the patch though. As a fix, it might make sense to save that > refactoring for a follow-on patch. Thanks, 65 lines diff file.
On 2/1/23 11:10 PM, Tian, Kevin wrote: >> From: Alex Williamson <alex.williamson@redhat.com> >> Sent: Thursday, February 2, 2023 7:28 AM >>> >>> +#ifdef CONFIG_HAVE_KVM >>> +static bool vfio_kvm_get_kvm_safe(struct vfio_device *device, struct kvm >> *kvm) >> >> I'm tempted to name these vfio_device_get_kvm_safe() and only pass the >> vfio_device, where of course we can get the kvm pointer from the group >> internally. >> > > I have a different thought. In the end the cdev series also need the similar > safe get/put logic then it's better to keep it in vfio_main.c called by > the group/cdev path individually. Ah, I hadn't considered the cdev series - OK, I can move the functions back into vfio_main and externalize both via drivers/vfio/vfio.h so they can be called from group.c for this fix and then available to vfio_main.c already for cdev.
diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c index bb24b2f0271e..52f434861294 100644 --- a/drivers/vfio/group.c +++ b/drivers/vfio/group.c @@ -13,6 +13,9 @@ #include <linux/vfio.h> #include <linux/iommufd.h> #include <linux/anon_inodes.h> +#ifdef CONFIG_HAVE_KVM +#include <linux/kvm_host.h> +#endif #include "vfio.h" static struct vfio { @@ -154,6 +157,55 @@ static int vfio_group_ioctl_set_container(struct vfio_group *group, return ret; } +#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); + device->put_kvm = NULL; + 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_group_open(struct vfio_device *device) { int ret; @@ -164,14 +216,32 @@ 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. */ + if (device->open_count == 0) { + spin_lock(&device->group->kvm_ref_lock); + if (device->group->kvm && + vfio_kvm_get_kvm_safe(device, device->group->kvm)) + device->kvm = device->group->kvm; + spin_unlock(&device->group->kvm_ref_lock); + } + ret = vfio_device_open(device, device->group->iommufd, device->group->kvm); + if (ret && device->kvm && device->open_count == 0) { + vfio_kvm_put_kvm(device); + device->kvm = NULL; + } + + mutex_unlock(&device->dev_set->lock); + out_unlock: mutex_unlock(&device->group->group_lock); return ret; @@ -180,7 +250,16 @@ 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->kvm && device->open_count == 0) { + vfio_kvm_put_kvm(device); + device->kvm = NULL; + } + + mutex_unlock(&device->dev_set->lock); mutex_unlock(&device->group->group_lock); } @@ -450,6 +529,7 @@ 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 +883,9 @@ 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..20c6bc249cb8 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, diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index 5177bb061b17..14dbf781ea8c 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -361,7 +361,6 @@ 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 +369,6 @@ 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 +385,6 @@ 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 +397,14 @@ 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 +412,12 @@ 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> --- 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 | 90 +++++++++++++++++++++++++++++++++++++--- drivers/vfio/vfio.h | 1 + drivers/vfio/vfio_main.c | 11 ++--- include/linux/vfio.h | 2 +- 4 files changed, 91 insertions(+), 13 deletions(-)