Hi Alex,
Here is the latest group_lock vs kvm lock deadlock fix + a non-fix
follow-on to remove the kvm argument from vfio_device_open and
vfio_device_first_open.
Changes from v3:
* Remove device->group->kvm reference in vfio_main by passing the
kvm in (Kevin)
* Slight re-organization to make it easier for cdev to build upon
this later and keep symmetry between get/put (Alex)
* Add follow-on patch that removes unused kvm argument (Yi)
Changes from v2:
* Relocate the new functions back to vfio_main and externalize to call
from group (Kevin) since cdev will need this too
* s/vfio_kvm_*_kvm/vfio_device_*_kvm/ and only pass device as input.
Handle new kvm_ref_lock directly inside vfio_device_get_kvm (Alex)
* Add assert_lockdep_held for dev_set lock (Alex)
* Internalize error paths for vfio_device_get_kvm_safe and now return
void - either device->kvm is set with a ref taken or is NULL (Alex)
* Other flow suggestions to make the call path cleaner - Thanks! (Alex)
* Can't pass group->kvm to vfio_device_open, as it references the value
outside of new lock. Pass device->kvm to minimize changes in this
fix (Alex, Yi)
Changes from v1:
* use spin_lock instead of spin_lock_irqsave (Jason)
* clear device->kvm_put as part of vfio_kvm_put_kvm (Yi)
* Re-arrange code to avoid referencing the group contents from within
vfio_main (Kevin) which meant moving most of the code in this patch
to group.c along with getting/dropping of the dev_set lock
Matthew Rosato (2):
vfio: fix deadlock between group lock and kvm lock
vfio: no need to pass kvm pointer during device open
drivers/vfio/group.c | 44 +++++++++++++++++++++----
drivers/vfio/vfio.h | 18 +++++++++--
drivers/vfio/vfio_main.c | 70 +++++++++++++++++++++++++++++++++-------
include/linux/vfio.h | 2 +-
4 files changed, 113 insertions(+), 21 deletions(-)
--
2.39.1
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 <[email protected]>
Suggested-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Matthew Rosato <[email protected]>
---
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;
--
2.39.1
Nothing uses this value during vfio_device_open anymore so it's safe
to remove it.
Signed-off-by: Matthew Rosato <[email protected]>
---
drivers/vfio/group.c | 2 +-
drivers/vfio/vfio.h | 3 +--
drivers/vfio/vfio_main.c | 7 +++----
3 files changed, 5 insertions(+), 7 deletions(-)
diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
index 98621ac082f0..0e9036e2b9c4 100644
--- a/drivers/vfio/group.c
+++ b/drivers/vfio/group.c
@@ -187,7 +187,7 @@ static int vfio_device_group_open(struct vfio_device *device)
if (device->open_count == 0)
vfio_device_group_get_kvm_safe(device);
- ret = vfio_device_open(device, device->group->iommufd, device->kvm);
+ ret = vfio_device_open(device, device->group->iommufd);
if (device->open_count == 0)
vfio_device_put_kvm(device);
diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
index 24d6cd285945..4f39ab549a80 100644
--- a/drivers/vfio/vfio.h
+++ b/drivers/vfio/vfio.h
@@ -18,8 +18,7 @@ struct vfio_container;
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 iommufd_ctx *iommufd);
void vfio_device_close(struct vfio_device *device,
struct iommufd_ctx *iommufd);
diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 28c47cd6a6b5..3a597e799918 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -397,7 +397,7 @@ static bool vfio_assert_device_open(struct vfio_device *device)
}
static int vfio_device_first_open(struct vfio_device *device,
- struct iommufd_ctx *iommufd, struct kvm *kvm)
+ struct iommufd_ctx *iommufd)
{
int ret;
@@ -444,8 +444,7 @@ 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 iommufd_ctx *iommufd)
{
int ret = 0;
@@ -453,7 +452,7 @@ int vfio_device_open(struct vfio_device *device,
device->open_count++;
if (device->open_count == 1) {
- ret = vfio_device_first_open(device, iommufd, kvm);
+ ret = vfio_device_first_open(device, iommufd);
if (ret)
device->open_count--;
}
--
2.39.1
> From: Matthew Rosato <[email protected]>
> Sent: Saturday, February 4, 2023 5:50 AM
> To: [email protected]; [email protected]; 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 <[email protected]>
> Suggested-by: Jason Gunthorpe <[email protected]>
> Signed-off-by: Matthew Rosato <[email protected]>
> ---
> 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 <[email protected]>
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 <[email protected]>
> Sent: Saturday, February 4, 2023 5:50 AM
>
> Nothing uses this value during vfio_device_open anymore so it's safe
> to remove it.
>
> Signed-off-by: Matthew Rosato <[email protected]>
> ---
> drivers/vfio/group.c | 2 +-
> drivers/vfio/vfio.h | 3 +--
> drivers/vfio/vfio_main.c | 7 +++----
> 3 files changed, 5 insertions(+), 7 deletions(-)
Reviewed-by: Yi Liu <[email protected]>
Regards,
Yi Liu
> diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> index 98621ac082f0..0e9036e2b9c4 100644
> --- a/drivers/vfio/group.c
> +++ b/drivers/vfio/group.c
> @@ -187,7 +187,7 @@ static int vfio_device_group_open(struct vfio_device
> *device)
> if (device->open_count == 0)
> vfio_device_group_get_kvm_safe(device);
>
> - ret = vfio_device_open(device, device->group->iommufd, device-
> >kvm);
> + ret = vfio_device_open(device, device->group->iommufd);
>
> if (device->open_count == 0)
> vfio_device_put_kvm(device);
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index 24d6cd285945..4f39ab549a80 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -18,8 +18,7 @@ struct vfio_container;
>
> 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 iommufd_ctx
> *iommufd);
> void vfio_device_close(struct vfio_device *device,
> struct iommufd_ctx *iommufd);
>
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 28c47cd6a6b5..3a597e799918 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -397,7 +397,7 @@ static bool vfio_assert_device_open(struct
> vfio_device *device)
> }
>
> static int vfio_device_first_open(struct vfio_device *device,
> - struct iommufd_ctx *iommufd, struct kvm
> *kvm)
> + struct iommufd_ctx *iommufd)
> {
> int ret;
>
> @@ -444,8 +444,7 @@ 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 iommufd_ctx
> *iommufd)
> {
> int ret = 0;
>
> @@ -453,7 +452,7 @@ int vfio_device_open(struct vfio_device *device,
>
> device->open_count++;
> if (device->open_count == 1) {
> - ret = vfio_device_first_open(device, iommufd, kvm);
> + ret = vfio_device_first_open(device, iommufd);
> if (ret)
> device->open_count--;
> }
> --
> 2.39.1
On Sat, 4 Feb 2023 06:21:48 +0000
"Liu, Yi L" <[email protected]> wrote:
> > From: Matthew Rosato <[email protected]>
> > Sent: Saturday, February 4, 2023 5:50 AM
> > To: [email protected]; [email protected]; 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 <[email protected]>
> > Suggested-by: Jason Gunthorpe <[email protected]>
> > Signed-off-by: Matthew Rosato <[email protected]>
> > ---
> > 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 <[email protected]>
>
> 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 <[email protected]>
> 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 <[email protected]>
> Suggested-by: Jason Gunthorpe <[email protected]>
> Signed-off-by: Matthew Rosato <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
> From: Matthew Rosato <[email protected]>
> Sent: Saturday, February 4, 2023 5:50 AM
>
> Nothing uses this value during vfio_device_open anymore so it's safe
> to remove it.
>
> Signed-off-by: Matthew Rosato <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
Tested-by: Tony Krowiak <[email protected]>
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 <[email protected]>
> Suggested-by: Jason Gunthorpe <[email protected]>
> Signed-off-by: Matthew Rosato <[email protected]>
> ---
> 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;
Tested-by: Tony Krowiak <[email protected]>
On 2/3/23 4:50 PM, Matthew Rosato wrote:
> Nothing uses this value during vfio_device_open anymore so it's safe
> to remove it.
>
> Signed-off-by: Matthew Rosato <[email protected]>
> ---
> drivers/vfio/group.c | 2 +-
> drivers/vfio/vfio.h | 3 +--
> drivers/vfio/vfio_main.c | 7 +++----
> 3 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
> index 98621ac082f0..0e9036e2b9c4 100644
> --- a/drivers/vfio/group.c
> +++ b/drivers/vfio/group.c
> @@ -187,7 +187,7 @@ static int vfio_device_group_open(struct vfio_device *device)
> if (device->open_count == 0)
> vfio_device_group_get_kvm_safe(device);
>
> - ret = vfio_device_open(device, device->group->iommufd, device->kvm);
> + ret = vfio_device_open(device, device->group->iommufd);
>
> if (device->open_count == 0)
> vfio_device_put_kvm(device);
> diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
> index 24d6cd285945..4f39ab549a80 100644
> --- a/drivers/vfio/vfio.h
> +++ b/drivers/vfio/vfio.h
> @@ -18,8 +18,7 @@ struct vfio_container;
>
> 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 iommufd_ctx *iommufd);
> void vfio_device_close(struct vfio_device *device,
> struct iommufd_ctx *iommufd);
>
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 28c47cd6a6b5..3a597e799918 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -397,7 +397,7 @@ static bool vfio_assert_device_open(struct vfio_device *device)
> }
>
> static int vfio_device_first_open(struct vfio_device *device,
> - struct iommufd_ctx *iommufd, struct kvm *kvm)
> + struct iommufd_ctx *iommufd)
> {
> int ret;
>
> @@ -444,8 +444,7 @@ 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 iommufd_ctx *iommufd)
> {
> int ret = 0;
>
> @@ -453,7 +452,7 @@ int vfio_device_open(struct vfio_device *device,
>
> device->open_count++;
> if (device->open_count == 1) {
> - ret = vfio_device_first_open(device, iommufd, kvm);
> + ret = vfio_device_first_open(device, iommufd);
> if (ret)
> device->open_count--;
> }
On Fri, 3 Feb 2023 16:50:25 -0500
Matthew Rosato <[email protected]> wrote:
> Hi Alex,
>
> Here is the latest group_lock vs kvm lock deadlock fix + a non-fix
> follow-on to remove the kvm argument from vfio_device_open and
> vfio_device_first_open.
>
> Changes from v3:
> * Remove device->group->kvm reference in vfio_main by passing the
> kvm in (Kevin)
> * Slight re-organization to make it easier for cdev to build upon
> this later and keep symmetry between get/put (Alex)
> * Add follow-on patch that removes unused kvm argument (Yi)
>
> Changes from v2:
> * Relocate the new functions back to vfio_main and externalize to call
> from group (Kevin) since cdev will need this too
> * s/vfio_kvm_*_kvm/vfio_device_*_kvm/ and only pass device as input.
> Handle new kvm_ref_lock directly inside vfio_device_get_kvm (Alex)
> * Add assert_lockdep_held for dev_set lock (Alex)
> * Internalize error paths for vfio_device_get_kvm_safe and now return
> void - either device->kvm is set with a ref taken or is NULL (Alex)
> * Other flow suggestions to make the call path cleaner - Thanks! (Alex)
> * Can't pass group->kvm to vfio_device_open, as it references the value
> outside of new lock. Pass device->kvm to minimize changes in this
> fix (Alex, Yi)
>
> Changes from v1:
> * use spin_lock instead of spin_lock_irqsave (Jason)
> * clear device->kvm_put as part of vfio_kvm_put_kvm (Yi)
> * Re-arrange code to avoid referencing the group contents from within
> vfio_main (Kevin) which meant moving most of the code in this patch
> to group.c along with getting/dropping of the dev_set lock
>
> Matthew Rosato (2):
> vfio: fix deadlock between group lock and kvm lock
> vfio: no need to pass kvm pointer during device open
>
> drivers/vfio/group.c | 44 +++++++++++++++++++++----
> drivers/vfio/vfio.h | 18 +++++++++--
> drivers/vfio/vfio_main.c | 70 +++++++++++++++++++++++++++++++++-------
> include/linux/vfio.h | 2 +-
> 4 files changed, 113 insertions(+), 21 deletions(-)
>
Applied to vfio next branch for v6.3. Thanks,
Alex