RE: [PATCH 08/10] iommu/ioasid: Introduce notifier APIs

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Sent: Thursday, March 26, 2020 1:55 AM
> 
> IOASID users fit into the publisher-subscriber pattern, a system wide
> blocking notifier chain can be used to inform subscribers of state
> changes. Notifier mechanism also abstracts publisher from knowing the
> private context each subcriber may have.
> 
> This patch adds APIs and a global notifier chain, a further optimization
> might be per set notifier for ioasid_set aware users.
> 
> Usage example:
> KVM register notifier block such that it can keep its guest-host PASID
> translation table in sync with any IOASID updates.
> 
> VFIO publish IOASID change by performing alloc/free, bind/unbind
> operations.
> 
> IOMMU driver gets notified when IOASID is freed by VFIO or core mm code
> such that PASID context can be cleaned up.

above example looks mixed. You have KVM registers the notifier but
finally having IOMMU driver to get notified... 😊

> 
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
>  drivers/iommu/ioasid.c | 61
> ++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/ioasid.h | 40 +++++++++++++++++++++++++++++++++
>  2 files changed, 101 insertions(+)
> 
> diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
> index 8612fe6477dc..27dce2cb5af2 100644
> --- a/drivers/iommu/ioasid.c
> +++ b/drivers/iommu/ioasid.c
> @@ -11,6 +11,22 @@
>  #include <linux/xarray.h>
> 
>  static DEFINE_XARRAY_ALLOC(ioasid_sets);
> +/*
> + * An IOASID could have multiple consumers. When a status change occurs,
> + * this notifier chain is used to keep them in sync. Each consumer of the
> + * IOASID service must register notifier block early to ensure no events
> + * are missed.
> + *
> + * This is a publisher-subscriber pattern where publisher can change the
> + * state of each IOASID, e.g. alloc/free, bind IOASID to a device and mm.
> + * On the other hand, subscribers gets notified for the state change and
> + * keep local states in sync.
> + *
> + * Currently, the notifier is global. A further optimization could be per
> + * IOASID set notifier chain.
> + */
> +static BLOCKING_NOTIFIER_HEAD(ioasid_chain);
> +
>  /**
>   * struct ioasid_set_data - Meta data about ioasid_set
>   *
> @@ -408,6 +424,7 @@ static void ioasid_free_locked(ioasid_t ioasid)
>  {
>  	struct ioasid_data *ioasid_data;
>  	struct ioasid_set_data *sdata;
> +	struct ioasid_nb_args args;
> 
>  	ioasid_data = xa_load(&active_allocator->xa, ioasid);
>  	if (!ioasid_data) {
> @@ -415,6 +432,13 @@ static void ioasid_free_locked(ioasid_t ioasid)
>  		return;
>  	}
> 
> +	args.id = ioasid;
> +	args.sid = ioasid_data->sdata->sid;
> +	args.pdata = ioasid_data->private;
> +	args.set_token = ioasid_data->sdata->token;
> +
> +	/* Notify all users that this IOASID is being freed */
> +	blocking_notifier_call_chain(&ioasid_chain, IOASID_FREE, &args);
>  	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) {
> @@ -624,6 +648,43 @@ int ioasid_find_sid(ioasid_t ioasid)
>  }
>  EXPORT_SYMBOL_GPL(ioasid_find_sid);
> 
> +int ioasid_add_notifier(struct notifier_block *nb)
> +{
> +	return blocking_notifier_chain_register(&ioasid_chain, nb);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_add_notifier);
> +
> +void ioasid_remove_notifier(struct notifier_block *nb)
> +{
> +	blocking_notifier_chain_unregister(&ioasid_chain, nb);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_remove_notifier);

register/unregister

> +
> +int ioasid_notify(ioasid_t ioasid, enum ioasid_notify_val cmd)

add a comment on when this function should be used?

> +{
> +	struct ioasid_data *ioasid_data;
> +	struct ioasid_nb_args args;
> +	int ret = 0;
> +
> +	mutex_lock(&ioasid_allocator_lock);
> +	ioasid_data = xa_load(&active_allocator->xa, ioasid);
> +	if (!ioasid_data) {
> +		pr_err("Trying to free unknown IOASID %u\n", ioasid);

why is it fixed to 'free'?

> +		mutex_unlock(&ioasid_allocator_lock);
> +		return -EINVAL;
> +	}
> +
> +	args.id = ioasid;
> +	args.sid = ioasid_data->sdata->sid;
> +	args.pdata = ioasid_data->private;

why no token info as did in ioasid_free?

> +
> +	ret = blocking_notifier_call_chain(&ioasid_chain, cmd, &args);
> +	mutex_unlock(&ioasid_allocator_lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_notify);
> +
>  MODULE_AUTHOR("Jean-Philippe Brucker <jean-
> philippe.brucker@arm.com>");
>  MODULE_AUTHOR("Jacob Pan <jacob.jun.pan@linux.intel.com>");
>  MODULE_DESCRIPTION("IO Address Space ID (IOASID) allocator");
> diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
> index e19c0ad93bd7..32d032913828 100644
> --- a/include/linux/ioasid.h
> +++ b/include/linux/ioasid.h
> @@ -4,6 +4,7 @@
> 
>  #include <linux/types.h>
>  #include <linux/errno.h>
> +#include <linux/notifier.h>
> 
>  #define INVALID_IOASID ((ioasid_t)-1)
>  #define INVALID_IOASID_SET (-1)
> @@ -30,6 +31,27 @@ struct ioasid_allocator_ops {
>  	void *pdata;
>  };
> 
> +/* Notification data when IOASID status changed */
> +enum ioasid_notify_val {
> +	IOASID_ALLOC = 1,
> +	IOASID_FREE,
> +	IOASID_BIND,
> +	IOASID_UNBIND,
> +};

Curious why IOASID_ALLOC is not notified aumatically within ioasid_alloc
similar to ioasid_free, while leaving to the publisher? BIND/UNBIND is
a publisher thing but a bit strange to see ALLOC/FREE with different policy here.

> +
> +/**
> + * struct ioasid_nb_args - Argument provided by IOASID core when notifier
> + * is called.
> + * @id:		the IOASID being notified
> + * @sid:	the IOASID set @id belongs to
> + * @pdata:	the private data attached to the IOASID
> + */
> +struct ioasid_nb_args {
> +	ioasid_t id;
> +	int sid;
> +	struct ioasid_set *set_token;
> +	void *pdata;
> +};
>  /* Shared IOASID set for reserved for host system use */
>  extern int system_ioasid_sid;
> 
> @@ -43,11 +65,15 @@ void *ioasid_find(int sid, ioasid_t ioasid, bool
> (*getter)(void *));
>  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);
> +int ioasid_add_notifier(struct notifier_block *nb);
> +void ioasid_remove_notifier(struct notifier_block *nb);
>  void ioasid_install_capacity(ioasid_t total);
>  int ioasid_alloc_system_set(int quota);
>  int ioasid_alloc_set(struct ioasid_set *token, ioasid_t quota, int *sid);
>  void ioasid_free_set(int sid, bool destroy_set);
>  int ioasid_find_sid(ioasid_t ioasid);
> +int ioasid_notify(ioasid_t id, enum ioasid_notify_val cmd);
> +
>  #else /* !CONFIG_IOASID */
>  static inline ioasid_t ioasid_alloc(int sid, ioasid_t min,
>  				    ioasid_t max, void *private)
> @@ -73,6 +99,20 @@ static inline void *ioasid_find(int sid, ioasid_t ioasid,
> bool (*getter)(void *)
>  	return NULL;
>  }
> 
> +static inline int ioasid_add_notifier(struct notifier_block *nb)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline void ioasid_remove_notifier(struct notifier_block *nb)
> +{
> +}
> +
> +int ioasid_notify(ioasid_t ioasid, enum ioasid_notify_val cmd)
> +{
> +	return -ENOTSUPP;
> +}
> +
>  static inline int ioasid_register_allocator(struct ioasid_allocator_ops
> *allocator)
>  {
>  	return -ENOTSUPP;
> --
> 2.7.4

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