Re: [PATCH v2 08/19] ioasid: Add custom IOASID allocator

[Auger Eric]

Hi Jacob,

On 4/24/19 1:31 AM, Jacob Pan 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. Xarray 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.
> 
> There can be multiple custom allocators registered but only one is
> used at a time. In case of hot removal of devices that provides the
> allocator, all IOASIDs must be freed prior to unregistering the
> allocator. Default XArray based allocator cannot be mixed with
> custom allocators, i.e. custom allocators will not be used if there
> are outstanding IOASIDs allocated by the default XA allocator.

What's the exact use case behind allowing several custom IOASID
allocators to be registered?
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
>  drivers/base/ioasid.c  | 182 ++++++++++++++++++++++++++++++++++++++++++++++---
>  include/linux/ioasid.h |  15 +++-
>  2 files changed, 187 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/base/ioasid.c b/drivers/base/ioasid.c
> index c4012aa..5cb36a4 100644
> --- a/drivers/base/ioasid.c
> +++ b/drivers/base/ioasid.c
> @@ -17,6 +17,120 @@ struct ioasid_data {
>  };
>  
>  static DEFINE_XARRAY_ALLOC(ioasid_xa);
> +static DEFINE_MUTEX(ioasid_allocator_lock);
> +static struct ioasid_allocator *ioasid_allocator;
A more explicit name may be chosen. If I understand correctly that's the
active_custom_allocator
> +
> +static LIST_HEAD(custom_allocators);
> +/*
> + * A flag to track if ioasid default allocator already been used, this will
is already in use?
> + * prevent custom allocator from being used. The reason is that custom allocator
s/The reason is that custom allocator/The reason is that custom allocators
> + * must have unadulterated space to track private data with xarray, there cannot
> + * be a mix been default and custom allocated IOASIDs.
> + */
> +static int default_allocator_used;
> +
> +/**
> + * ioasid_register_allocator - register a custom allocator
> + * @allocator: the custom allocator to be registered
> + *
> + * Custom allocator take precedence over the default xarray based allocator.
> + * Private data associated with the ASID are managed by ASID common code
> + * similar to data stored in xa.
> + *
> + * There can be multiple allocators registered but only one is active. In case
> + * of runtime removal of an custom allocator, the next one is activated based
> + * on the registration ordering.
This last sentence may be moved to the unregister() kerneldoc
> + */
> +int ioasid_register_allocator(struct ioasid_allocator *allocator)
> +{
> +	struct ioasid_allocator *pallocator;
> +	int ret = 0;
> +
> +	if (!allocator)
> +		return -EINVAL;
> +
> +	mutex_lock(&ioasid_allocator_lock);
> +	if (list_empty(&custom_allocators))
> +		ioasid_allocator = allocator;
The fact the first registered custom allocator gets automatically active
was not obvious to me and may deserve a comment.
> +	else {
> +		/* Check if the allocator is already registered */
> +		list_for_each_entry(pallocator, &custom_allocators, list) {
> +			if (pallocator == allocator) {
> +				pr_err("IOASID allocator already exist\n");
s/exist/registered?
> +				ret = -EEXIST;
> +				goto out_unlock;
> +			}
> +		}
> +	}
> +	list_add_tail(&allocator->list, &custom_allocators);
> +
> +out_unlock:
> +	mutex_unlock(&ioasid_allocator_lock);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_register_allocator);
> +
> +/**
> + * ioasid_unregister_allocator - Remove a custom IOASID allocator
> + * @allocator: the custom allocator to be removed
> + *
> + * Remove an allocator from the list, activate the next allocator in
> + * the order it was  registration.
> + */
> +void ioasid_unregister_allocator(struct ioasid_allocator *allocator)
> +{
> +	if (!allocator)
> +		return;
> +
> +	if (list_empty(&custom_allocators)) {
> +		pr_warn("No custom IOASID allocators active!\n");
s/active/registered?
> +		return;
> +	}
> +
> +	mutex_lock(&ioasid_allocator_lock);
> +	list_del(&allocator->list);
> +	if (list_empty(&custom_allocators)) {
> +		pr_info("No custom IOASID allocators\n");
> +		/*
> +		 * All IOASIDs should have been freed before the last allocator
> +		 * is unregistered.
> +		 */
> +		BUG_ON(!xa_empty(&ioasid_xa));
At this stage it is difficult to assess whether using a BUG_ON() is safe
here. Who is responsible for freeing the IOASIDs?
> +		ioasid_allocator = NULL;
> +	} else if (allocator == ioasid_allocator) {
> +		ioasid_allocator = list_entry(&custom_allocators, struct ioasid_allocator, list);
> +		pr_info("IOASID allocator changed");
> +	}
> +	mutex_unlock(&ioasid_allocator_lock);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_unregister_allocator);
> +
> +/**
> + * ioasid_set_data - Set private data for an allocated ioasid
> + * @ioasid: the ID to set data
> + * @data:   the private data
> + *
> + * 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;
> +
> +	ioasid_data = xa_load(&ioasid_xa, ioasid);
> +	if (ioasid_data)
> +		ioasid_data->private = data;
> +	else
> +		ret = -ENOENT;
> +
> +	/* getter may use the private data */
> +	synchronize_rcu();
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_set_data);
> +
>  /**
>   * ioasid_alloc - Allocate an IOASID
>   * @set: the IOASID set
> @@ -31,7 +145,7 @@ static DEFINE_XARRAY_ALLOC(ioasid_xa);
>  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);
> @@ -40,14 +154,37 @@ 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 use default.
> +	 * However, if there are active IOASIDs already been allocated by default
> +	 * allocator, custom allocator cannot be used.
> +	 */
> +	if (!default_allocator_used && ioasid_allocator) {
> +		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 XA to manage private data also sanitiy check custom> +		 * allocator for duplicates.
s/data also sanitiy check/data, also sanity check
> +		 */
> +		min = id;
> +		max = id + 1;
> +	} else
> +		default_allocator_used = 1;
shouldn't default_allocator_used be protected as well?
> +
>  	if (xa_alloc(&ioasid_xa, &id, data, XA_LIMIT(min, max), GFP_KERNEL)) {
>  		pr_err("Failed to alloc ioasid from %d to %d\n", min, max);
>  		goto exit_free;
>  	}
> -
>  	data->id = id;
wouldn't it be possible to integrate the default io asid allocator as
any custom allocator, ie. implement an alloc callback using xa_alloc.
Then the active io allocator could be either a custom or a default one.
> +
>  exit_free:
> -	if (id < 0) {
> +	if (id < 0 || id == INVALID_IOASID) {
>  		kfree(data);
>  		return INVALID_IOASID;
>  	}
> @@ -59,12 +196,29 @@ 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) {
> +		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;
> +	}
>  
>  	ioasid_data = xa_erase(&ioasid_xa, ioasid);
> +
>  	kfree_rcu(ioasid_data, rcu);
> +
> +	if (xa_empty(&ioasid_xa))
> +		default_allocator_used = 0;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(ioasid_free);
>  
> @@ -79,7 +233,8 @@ 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.
s/not belong/does not belong
>   */
>  void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
>  		  bool (*getter)(void *))
> @@ -89,11 +244,20 @@ void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
>  
>  	rcu_read_lock();
>  	ioasid_data = xa_load(&ioasid_xa, 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..e773c13 100644
> --- a/include/linux/ioasid.h
> +++ b/include/linux/ioasid.h
> @@ -5,20 +5,33 @@
>  #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;
> +	struct list_head list;
> +};
> +
>  #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);
you need to change the definition for the !CONFIG_IOASID case too
>  
>  void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
>  		  bool (*getter)(void *));
> +int ioasid_register_allocator(struct ioasid_allocator *allocator);
> +void ioasid_unregister_allocator(struct ioasid_allocator *allocator);
> +
> +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,
Just to make sure, don't you need to define the new functions if
!CONFIG_IOASID?

Thanks

Eric
>