Date:   Tue, 31 Mar 2020 08:13:29 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 08/10] iommu/ioasid: Introduce notifier APIs

On Sat, 28 Mar 2020 06:43:37 +0000
"Tian, Kevin" <kevin.tian@...el.com> wrote:

> > From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > Sent: Saturday, March 28, 2020 2:37 AM
> > 
> > On Fri, 27 Mar 2020 10:03:26 +0000
> > "Tian, Kevin" <kevin.tian@...el.com> wrote:
> >   
> > > > From: Jacob Pan <jacob.jun.pan@...ux.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@...el.com>
> > > > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.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@....com>");  
> > > >  MODULE_AUTHOR("Jacob Pan <jacob.jun.pan@...ux.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? 
> 

Sounds good. I will change it to:

/*
 * Notification event when IOASID status changed. Note that there is no
 * event for ALLOC in that the allocator is the only one knows about the
 * new IOASID.
 */
enum ioasid_notify_val {
	IOASID_FREE = 1,
	IOASID_BIND,
	IOASID_UNBIND,
};

> >   
> > > > +
> > > > +/**
> > > > + * 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]  

[Jacob Pan]

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