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

[Lu Baolu <baolu.lu@linux.intel.com>]

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@linaro.org>
> ---
> 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@linux.intel.com>

Best regards,
baolu