Re: [PATCH v7 02/24] iommu/ioasid: Add ioasid references

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On 5/20/20 1:54 AM, Jean-Philippe Brucker wrote:
Let IOASID users take references to existing ioasids with ioasid_get().
ioasid_put() drops a reference and only frees the ioasid when its
reference number is zero. It returns true if the ioasid was freed.
For drivers that don't call ioasid_get(), ioasid_put() is the same as
ioasid_free().

Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
---
v6->v7: rename ioasid_free() to ioasid_put(), add WARN in ioasid_get()
---
  include/linux/ioasid.h      | 10 ++++++++--
  drivers/iommu/intel-iommu.c |  4 ++--
  drivers/iommu/intel-svm.c   |  6 +++---
  drivers/iommu/ioasid.c      | 38 +++++++++++++++++++++++++++++++++----
  4 files changed, 47 insertions(+), 11 deletions(-)

diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
index 6f000d7a0ddc..e9dacd4b9f6b 100644
--- a/include/linux/ioasid.h
+++ b/include/linux/ioasid.h
@@ -34,7 +34,8 @@ struct ioasid_allocator_ops {
  #if IS_ENABLED(CONFIG_IOASID)
  ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
  		      void *private);
-void ioasid_free(ioasid_t ioasid);
+void ioasid_get(ioasid_t ioasid);
+bool ioasid_put(ioasid_t ioasid);
  void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
  		  bool (*getter)(void *));
  int ioasid_register_allocator(struct ioasid_allocator_ops *allocator);
@@ -48,10 +49,15 @@ static inline ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min,
  	return INVALID_IOASID;
  }
-static inline void ioasid_free(ioasid_t ioasid)
+static inline void ioasid_get(ioasid_t ioasid)
  {
  }
+static inline bool ioasid_put(ioasid_t ioasid)
+{
+	return false;
+}
+
  static inline void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
  				bool (*getter)(void *))
  {
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index ed21ce6d1238..0230f35480ee 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -5432,7 +5432,7 @@ static void auxiliary_unlink_device(struct dmar_domain *domain,
  	domain->auxd_refcnt--;
if (!domain->auxd_refcnt && domain->default_pasid > 0)
-		ioasid_free(domain->default_pasid);
+		ioasid_put(domain->default_pasid);
  }
static int aux_domain_add_dev(struct dmar_domain *domain,
@@ -5494,7 +5494,7 @@ static int aux_domain_add_dev(struct dmar_domain *domain,
  	spin_unlock(&iommu->lock);
  	spin_unlock_irqrestore(&device_domain_lock, flags);
  	if (!domain->auxd_refcnt && domain->default_pasid > 0)
-		ioasid_free(domain->default_pasid);
+		ioasid_put(domain->default_pasid);
return ret;
  }
diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
index 2998418f0a38..86f1264bd07c 100644
--- a/drivers/iommu/intel-svm.c
+++ b/drivers/iommu/intel-svm.c
@@ -353,7 +353,7 @@ int intel_svm_bind_mm(struct device *dev, int *pasid, int flags, struct svm_dev_
  		if (mm) {
  			ret = mmu_notifier_register(&svm->notifier, mm);
  			if (ret) {
-				ioasid_free(svm->pasid);
+				ioasid_put(svm->pasid);
  				kfree(svm);
  				kfree(sdev);
  				goto out;
@@ -371,7 +371,7 @@ int intel_svm_bind_mm(struct device *dev, int *pasid, int flags, struct svm_dev_
  		if (ret) {
  			if (mm)
  				mmu_notifier_unregister(&svm->notifier, mm);
-			ioasid_free(svm->pasid);
+			ioasid_put(svm->pasid);
  			kfree(svm);
  			kfree(sdev);
  			goto out;
@@ -447,7 +447,7 @@ int intel_svm_unbind_mm(struct device *dev, int pasid)
  			kfree_rcu(sdev, rcu);
if (list_empty(&svm->devs)) {
-				ioasid_free(svm->pasid);
+				ioasid_put(svm->pasid);
  				if (svm->mm)
  					mmu_notifier_unregister(&svm->notifier, svm->mm);
  				list_del(&svm->list);
diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
index 0f8dd377aada..50ee27bbd04e 100644
--- a/drivers/iommu/ioasid.c
+++ b/drivers/iommu/ioasid.c
@@ -2,7 +2,7 @@
  /*
   * I/O Address Space ID allocator. There is one global IOASID space, split into
   * subsets. Users create a subset with DECLARE_IOASID_SET, then allocate and
- * free IOASIDs with ioasid_alloc and ioasid_free.
+ * free IOASIDs with ioasid_alloc and ioasid_put.
   */
  #include <linux/ioasid.h>
  #include <linux/module.h>
@@ -15,6 +15,7 @@ struct ioasid_data {
  	struct ioasid_set *set;
  	void *private;
  	struct rcu_head rcu;
+	refcount_t refs;
  };
/*
@@ -314,6 +315,7 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
data->set = set;
  	data->private = private;
+	refcount_set(&data->refs, 1);
/*
  	 * Custom allocator needs allocator data to perform platform specific
@@ -346,11 +348,34 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
  EXPORT_SYMBOL_GPL(ioasid_alloc);
/**
- * ioasid_free - Free an IOASID
+ * ioasid_get - obtain a reference to the IOASID
+ */
+void ioasid_get(ioasid_t ioasid)
+{
+	struct ioasid_data *ioasid_data;
+
+	spin_lock(&ioasid_allocator_lock);
+	ioasid_data = xa_load(&active_allocator->xa, ioasid);
+	if (ioasid_data)
+		refcount_inc(&ioasid_data->refs);
+	else
+		WARN_ON(1);
+	spin_unlock(&ioasid_allocator_lock);
+}
+EXPORT_SYMBOL_GPL(ioasid_get);
+
+/**
+ * ioasid_put - Release a reference to an ioasid
   * @ioasid: the ID to remove
+ *
+ * Put a reference to the IOASID, free it when the number of references drops to
+ * zero.
+ *
+ * Return: %true if the IOASID was freed, %false otherwise.
   */
-void ioasid_free(ioasid_t ioasid)
+bool ioasid_put(ioasid_t ioasid)
  {
+	bool free = false;
  	struct ioasid_data *ioasid_data;
spin_lock(&ioasid_allocator_lock);
@@ -360,6 +385,10 @@ void ioasid_free(ioasid_t ioasid)
  		goto exit_unlock;
  	}
+ free = refcount_dec_and_test(&ioasid_data->refs);
+	if (!free)
+		goto exit_unlock;
+
  	active_allocator->ops->free(ioasid, active_allocator->ops->pdata);
  	/* Custom allocator needs additional steps to free the xa element */
  	if (active_allocator->flags & IOASID_ALLOCATOR_CUSTOM) {
@@ -369,8 +398,9 @@ void ioasid_free(ioasid_t ioasid)
exit_unlock:
  	spin_unlock(&ioasid_allocator_lock);
+	return free;
  }
-EXPORT_SYMBOL_GPL(ioasid_free);
+EXPORT_SYMBOL_GPL(ioasid_put);
/**
   * ioasid_find - Find IOASID data


Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>

Best regards,
baolu



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