[PATCH V4 03/18] iommu/ioasid: Add a separate function for detach data

Jacob Pan
2021-02-27T22:01:11Z

IOASID private data can be cleared by ioasid_attach_data() with a NULL
data pointer. A common use case is for a caller to free the data
afterward. ioasid_attach_data() calls synchronize_rcu() before return
such that free data can be sure without outstanding readers.
However, since synchronize_rcu() may sleep, ioasid_attach_data() cannot
be used under spinlocks.

This patch adds ioasid_detach_data() as a separate API where
synchronize_rcu() is called only in this case. ioasid_attach_data() can
then be used under spinlocks. In addition, this change makes the API
symmetrical.

Signed-off-by: Jacob Pan <jacob.jun.pan-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
---
drivers/iommu/intel/svm.c | 4 +--
drivers/iommu/ioasid.c | 54 +++++++++++++++++++++++++++++++--------
include/linux/ioasid.h | 5 +++-
3 files changed, 50 insertions(+), 13 deletions(-)

diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 0053df9edffc..68372a7eb8b5 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -425,7 +425,7 @@ int intel_svm_bind_gpasid(struct iommu_domain *domain, struct device *dev,
list_add_rcu(&sdev->list, &svm->devs);
out:
if (!IS_ERR_OR_NULL(svm) && list_empty(&svm->devs)) {
- ioasid_attach_data(data->hpasid, NULL);
+ ioasid_detach_data(data->hpasid);
kfree(svm);
}

@@ -468,7 +468,7 @@ int intel_svm_unbind_gpasid(struct device *dev, u32 pasid)
* the unbind, IOMMU driver will get notified
* and perform cleanup.
*/
- ioasid_attach_data(pasid, NULL);
+ ioasid_detach_data(pasid);
kfree(svm);
}
}
diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
index eeadf4586e0a..4eb9b3dd1b85 100644
--- a/drivers/iommu/ioasid.c
+++ b/drivers/iommu/ioasid.c
@@ -273,23 +273,57 @@ int ioasid_attach_data(ioasid_t ioasid, void *data)

spin_lock(&ioasid_allocator_lock);
ioasid_data = xa_load(&active_allocator->xa, ioasid);
- if (ioasid_data)
- rcu_assign_pointer(ioasid_data->private, data);
- else
+
+ if (!ioasid_data) {
ret = -ENOENT;
- spin_unlock(&ioasid_allocator_lock);
+ goto done_unlock;
+ }

- /*
- * Wait for readers to stop accessing the old private data, so the
- * caller can free it.
- */
- if (!ret)
- synchronize_rcu();
+ if (ioasid_data->private) {
+ ret = -EBUSY;
+ goto done_unlock;
+ }
+ rcu_assign_pointer(ioasid_data->private, data);
+
+done_unlock:
+ spin_unlock(&ioasid_allocator_lock);

return ret;
}
EXPORT_SYMBOL_GPL(ioasid_attach_data);

+/**
+ * ioasid_detach_data - Clear the private data of an ioasid
+ *
+ * @ioasid: the IOASIDD to clear private data
+ */
+void ioasid_detach_data(ioasid_t ioasid)
+{
+ struct ioasid_data *ioasid_data;
+
+ spin_lock(&ioasid_allocator_lock);
+ ioasid_data = xa_load(&active_allocator->xa, ioasid);
+
+ if (!ioasid_data) {
+ pr_warn("IOASID %u not found to detach data from\n", ioasid);
+ goto done_unlock;
+ }
+
+ if (ioasid_data->private) {
+ rcu_assign_pointer(ioasid_data->private, NULL);
+ goto done_unlock;
+ }
+
+done_unlock:
+ spin_unlock(&ioasid_allocator_lock);
+ /*
+ * Wait for readers to stop accessing the old private data,
+ * so the caller can free it.
+ */
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(ioasid_detach_data);
+
/**
* ioasid_alloc - Allocate an IOASID
* @set: the IOASID set
diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
index 60ea279802b8..f6e705f832f0 100644
--- a/include/linux/ioasid.h
+++ b/include/linux/ioasid.h
@@ -41,7 +41,7 @@ void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
int ioasid_register_allocator(struct ioasid_allocator_ops *allocator);
void ioasid_unregister_allocator(struct ioasid_allocator_ops *allocator);
int ioasid_attach_data(ioasid_t ioasid, void *data);
-
+void ioasid_detach_data(ioasid_t ioasid);
#else /* !CONFIG_IOASID */
static inline ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min,
ioasid_t max, void *private)
@@ -78,5 +78,8 @@ static inline int ioasid_attach_data(ioasid_t ioasid, void *data)
return -ENOTSUPP;
}

+static inline void ioasid_detach_data(ioasid_t ioasid)
+{
+}
#endif /* CONFIG_IOASID */
#endif /* __LINUX_IOASID_H */
--
2.25.1