Re: [PATCH 02/18] ioasid: Add custom IOASID allocator

[Alex Williamson]

On Mon,  8 Apr 2019 16:59:17 -0700
Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx> wrote:

> Sometimes, IOASID allocation must be handled by platform specific
> code. The use cases are guest vIOMMU and pvIOMMU where IOASIDs need
> to be allocated by the host via enlightened or paravirt interfaces.
> 
> This patch adds an extension to the IOASID allocator APIs such that
> platform drivers can register a custom allocator, possibly at boot
> time, to take over the allocation. IDR is still used for tracking
> and searching purposes internal to the IOASID code. Private data of
> an IOASID can also be set after the allocation.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
>  drivers/base/ioasid.c  | 124 +++++++++++++++++++++++++++++++++++++++++++++----
>  include/linux/ioasid.h |  28 ++++++++++-
>  2 files changed, 143 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/base/ioasid.c b/drivers/base/ioasid.c
> index cf122b2..294e856 100644
> --- a/drivers/base/ioasid.c
> +++ b/drivers/base/ioasid.c
> @@ -17,6 +17,74 @@ struct ioasid_data {
>  };
>  
>  static DEFINE_IDR(ioasid_idr);
> +static DEFINE_MUTEX(ioasid_allocator_lock);
> +static const struct ioasid_allocator *ioasid_allocator;
> +
> +
> +/**
> + * ioasid_set_allocator - register a custom allocator
> + *
> + * Custom allocator take precedence over the default IDR based allocator.
> + * Private data associated with the ASID are managed by ASID common code
> + * similar to IDR data.
> + */
> +int ioasid_set_allocator(struct ioasid_allocator *allocator)
> +{
> +	int ret = 0;
> +
> +	if (!allocator)
> +		return -EINVAL;
> +
> +	mutex_lock(&ioasid_allocator_lock);
> +	if (ioasid_allocator) {
> +		ret = -EBUSY;
> +		goto exit_unlock;
> +	}
> +	ioasid_allocator = allocator;
> +
> +exit_unlock:
> +	mutex_unlock(&ioasid_allocator_lock);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_set_allocator);

Should this fault if there are existing idr's allocated?

> +
> +/**
> + * ioasid_clear_allocator - Free the custom IOASID allocator
> + *
> + * REVISIT: So far there is only one custom allocator allowed.
> + */
> +void ioasid_clear_allocator(void)
> +{
> +	mutex_lock(&ioasid_allocator_lock);
> +	ioasid_allocator = NULL;
> +	mutex_unlock(&ioasid_allocator_lock);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_clear_allocator);
> +
> +/**
> + * ioasid_set_data - Set private data for an allocated ioasid
> + *
> + * For IOASID that is already allocated, private data can be set
> + * via this API. Future lookup can be done via ioasid_find.
> + */
> +int ioasid_set_data(ioasid_t ioasid, void *data)
> +{
> +	struct ioasid_data *ioasid_data;
> +	int ret = 0;
> +
> +	idr_lock(&ioasid_idr);
> +	ioasid_data = idr_find(&ioasid_idr, ioasid);
> +	if (ioasid_data)
> +		ioasid_data->private = data;
> +	else
> +		ret = -ENOENT;
> +	idr_unlock(&ioasid_idr);
> +	/* getter may use the private data */
> +	synchronize_rcu();
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_set_data);
>  
>  /**
>   * ioasid_alloc - Allocate an IOASID
> @@ -32,7 +100,7 @@ static DEFINE_IDR(ioasid_idr);
>  ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
>  		      void *private)
>  {
> -	int id = -1;
> +	int id = INVALID_IOASID;
>  	struct ioasid_data *data;
>  
>  	data = kzalloc(sizeof(*data), GFP_KERNEL);
> @@ -42,13 +110,30 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
>  	data->set = set;
>  	data->private = private;
>  
> +	/* Use custom allocator if available, otherwise default to IDR */
> +	if (ioasid_allocator) {

If this races with ioasid_clear_allocator() ioasid_allocator might be
set above, but NULL below to generate a segfault.  If this races with
ioasid_set_allocator() an id can be allocated that the custom allocator
doesn't track.

> +		mutex_lock(&ioasid_allocator_lock);
> +		id = ioasid_allocator->alloc(min, max, ioasid_allocator->pdata);
> +		mutex_unlock(&ioasid_allocator_lock);
> +		if (id == INVALID_IOASID) {
> +			pr_err("Failed ASID allocation by custom allocator\n");
> +			goto exit_free;
> +		}
> +		/*
> +		 * Use IDR to manage private data also sanitiy check custom
> +		 * allocator for duplicates.
> +		 */
> +		min = id;
> +		max = id + 1;
> +	}
>  	idr_preload(GFP_KERNEL);
>  	idr_lock(&ioasid_idr);
>  	data->id = id = idr_alloc(&ioasid_idr, data, min, max, GFP_ATOMIC);
>  	idr_unlock(&ioasid_idr);
>  	idr_preload_end();
>  
> -	if (id < 0) {
> +exit_free:
> +	if (id < 0 || id == INVALID_IOASID) {
>  		kfree(data);

What if an ioasid is already allocated before the ioasid_allocator is
registered?  The .alloc callback above could return an id that
idr_alloc cannot provide, in which case this cleanup does not call the
custom allocator's free callback.

>  		return INVALID_IOASID;
>  	}
> @@ -60,9 +145,20 @@ EXPORT_SYMBOL_GPL(ioasid_alloc);
>   * ioasid_free - Free an IOASID
>   * @ioasid: the ID to remove
>   */
> -void ioasid_free(ioasid_t ioasid)
> +int ioasid_free(ioasid_t ioasid)
>  {
>  	struct ioasid_data *ioasid_data;
> +	int ret = 0;
> +
> +	if (ioasid_allocator) {

Same races as above.

> +		mutex_lock(&ioasid_allocator_lock);
> +		ret = ioasid_allocator->free(ioasid, ioasid_allocator->pdata);
> +		mutex_unlock(&ioasid_allocator_lock);
> +	}
> +	if (ret) {
> +		pr_err("ioasid %d custom allocator free failed\n", ioasid);
> +		return ret;
> +	}
>  
>  	idr_lock(&ioasid_idr);
>  	ioasid_data = idr_remove(&ioasid_idr, ioasid);
> @@ -70,6 +166,8 @@ void ioasid_free(ioasid_t ioasid)
>  
>  	if (ioasid_data)
>  		kfree_rcu(ioasid_data, rcu);
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(ioasid_free);
>  
> @@ -84,7 +182,8 @@ EXPORT_SYMBOL_GPL(ioasid_free);
>   * if @getter returns false, then the object is invalid and NULL is returned.
>   *
>   * If the IOASID has been allocated for this set, return the private pointer
> - * passed to ioasid_alloc. Otherwise return NULL.
> + * passed to ioasid_alloc. Private data can be NULL if not set. Return an error
> + * if the IOASID is not found or not belong to the set.
>   */
>  void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
>  		  bool (*getter)(void *))
> @@ -94,11 +193,20 @@ void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
>  
>  	rcu_read_lock();
>  	ioasid_data = idr_find(&ioasid_idr, ioasid);
> -	if (ioasid_data && ioasid_data->set == set) {
> -		priv = ioasid_data->private;
> -		if (getter && !getter(priv))
> -			priv = NULL;
> +	if (!ioasid_data) {
> +		priv = ERR_PTR(-ENOENT);
> +		goto unlock;
> +	}
> +	if (set && ioasid_data->set != set) {
> +		/* data found but does not belong to the set */
> +		priv = ERR_PTR(-EACCES);
> +		goto unlock;
>  	}
> +	/* Now IOASID and its set is verified, we can return the private data */
> +	priv = ioasid_data->private;
> +	if (getter && !getter(priv))
> +		priv = NULL;
> +unlock:
>  	rcu_read_unlock();
>  
>  	return priv;
> diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
> index 6f3655a..64994e7 100644
> --- a/include/linux/ioasid.h
> +++ b/include/linux/ioasid.h
> @@ -5,20 +5,31 @@
>  #define INVALID_IOASID ((ioasid_t)-1)
>  typedef unsigned int ioasid_t;
>  typedef int (*ioasid_iter_t)(ioasid_t ioasid, void *private, void *data);
> +typedef ioasid_t (*ioasid_alloc_fn_t)(ioasid_t min, ioasid_t max, void *data);
> +typedef int (*ioasid_free_fn_t)(ioasid_t ioasid, void *data);
>  
>  struct ioasid_set {
>  	int dummy;
>  };
>  
> +struct ioasid_allocator {
> +	ioasid_alloc_fn_t alloc;
> +	ioasid_free_fn_t free;
> +	void *pdata;
> +};
> +
>  #define DECLARE_IOASID_SET(name) struct ioasid_set name = { 0 }
>  
>  #ifdef CONFIG_IOASID
>  ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
>  		      void *private);
> -void ioasid_free(ioasid_t ioasid);
> +int ioasid_free(ioasid_t ioasid);
>  
>  void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
>  		  bool (*getter)(void *));
> +int ioasid_set_allocator(struct ioasid_allocator *allocator);
> +void ioasid_clear_allocator(void);
> +int ioasid_set_data(ioasid_t ioasid, void *data);
>  
>  #else /* !CONFIG_IOASID */
>  static inline ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min,
> @@ -36,5 +47,20 @@ static inline void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
>  {
>  	return NULL;
>  }
> +
> +static inline int ioasid_set_allocator(struct ioasid_allocator *allocator)
> +{
> +	return -EINVAL;
> +}
> +
> +static inline void ioasid_clear_allocator(void)
> +{
> +}
> +
> +static inline int ioasid_set_data(ioasid_t ioasid, void *data)
> +{
> +	return -EINVAL;
> +}
> +
>  #endif /* CONFIG_IOASID */
>  #endif /* __LINUX_IOASID_H */