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: Saturday, March 28, 2020 2:37 AM
> 
> On Fri, 27 Mar 2020 10:03:26 +0000
> "Tian, Kevin" <kevin.tian@intel.com> wrote:
> 
> > > 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... 😊
> >
> Right, felt like a tale of two subscribers got mixed. I meant to list a
> few use cases with publisher and subscriber roles separate.
> I will change that to "Usage examples", and explicit state each role.
> 
> > >
> > > 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
> >
> Sounds good.
> 
> > > +
> > > +int ioasid_notify(ioasid_t ioasid, enum ioasid_notify_val cmd)
> >
> > add a comment on when this function should be used?
> >
> Sure, how about:
> /**
>  * ioasid_notify - Send notification on a given IOASID for status change.
>  *                 Used by publishers when the status change may affect
>  *                 subscriber's internal state.
>  *
>  * @ioasid:	The IOASID to which the notification will send
>  * @cmd:	The notification event
>  *
>  */

looks good.

> 
> > > +{
> > > +	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'?
> >
> Good catch, it shouldn;t be just free. It was a relic of early test
> case.
> 
> > > +		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?
> >
> Good catch, should include token as well. It is better to include all
> the data such that subscribers don't have to do any lookup which may
> cause race.
> 
> > > +
> > > +	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.
> >
> I don't see a use case for ALLOC notification yet. Any user does the
> allocation would the be the first and only one know about this IOASID.
> 
> Unless we have set level notifier, which may be interested in a new
> IOASID being allocated within the set.

then remove this type until it is actually required when supporting
set-level notifier? 

> 
> > > +
> > > +/**
> > > + * 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
> >
> 
> [Jacob Pan]