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Date:   Wed, 9 Sep 2020 15:58:08 -0700
From:   Jacob Pan <jacob.jun.pan@linux.intel.com>
To:     Auger Eric <eric.auger@redhat.com>
Cc:     Jacob Pan <jacob.pan.linux@gmail.com>,
        iommu@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        David Woodhouse <dwmw2@infradead.org>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Raj Ashok <ashok.raj@intel.com>, Wu Hao <hao.wu@intel.com>,
        jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH v2 6/9] iommu/ioasid: Introduce notification APIs
Message-ID: <20200909155808.3964dcad@jacob-builder>
In-Reply-To: <9cfcfbd5-fa1b-2e3f-d7fb-44215f7be744@redhat.com>
References: <1598070918-21321-1-git-send-email-jacob.jun.pan@linux.intel.com>
        <1598070918-21321-7-git-send-email-jacob.jun.pan@linux.intel.com>
        <9cfcfbd5-fa1b-2e3f-d7fb-44215f7be744@redhat.com>
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On Tue, 1 Sep 2020 18:49:38 +0200
Auger Eric <eric.auger@redhat.com> wrote:

> Hi Jacob,
> 
> On 8/22/20 6:35 AM, Jacob Pan wrote:
> > Relations among IOASID users largely follow a publisher-subscriber
> > pattern. E.g. to support guest SVA on Intel Scalable I/O
> > Virtualization (SIOV) enabled platforms, VFIO, IOMMU, device
> > drivers, KVM are all users of IOASIDs. When a state change occurs,
> > VFIO publishes the change event that needs to be processed by other
> > users/subscribers.
> > 
> > This patch introduced two types of notifications: global and per
> > ioasid_set. The latter is intended for users who only needs to
> > handle events related to the IOASID of a given set.
> > For more information, refer to the kernel documentation at
> > Documentation/ioasid.rst.
> > 
> > Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> > Signed-off-by: Wu Hao <hao.wu@intel.com>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > ---
> >  drivers/iommu/ioasid.c | 280
> > ++++++++++++++++++++++++++++++++++++++++++++++++-
> > include/linux/ioasid.h |  70 +++++++++++++ 2 files changed, 348
> > insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
> > index c0aef38a4fde..6ddc09a7fe74 100644
> > --- a/drivers/iommu/ioasid.c
> > +++ b/drivers/iommu/ioasid.c
> > @@ -9,8 +9,35 @@
> >  #include <linux/spinlock.h>
> >  #include <linux/xarray.h>
> >  #include <linux/ioasid.h>
> > +#include <linux/sched/mm.h>
> >  
> >  static DEFINE_XARRAY_ALLOC(ioasid_sets);
> > +/*
> > + * An IOASID could have multiple consumers where each consumeer
> > may have  
> can have multiple consumers
Sounds good, I used past tense to describe a possibility :)

> > + * hardware contexts associated with IOASIDs.
> > + * When a status change occurs, such as IOASID is being freed,
> > notifier chains  
> s/such as IOASID is being freed/, like on IOASID deallocation,
Better, will do.

> > + * are used to keep the consumers in sync.
> > + * 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 ATOMIC_NOTIFIER_HEAD(ioasid_chain);
> > +
> > +/* List to hold pending notification block registrations */
> > +static LIST_HEAD(ioasid_nb_pending_list);
> > +static DEFINE_SPINLOCK(ioasid_nb_lock);
> > +struct ioasid_set_nb {
> > +	struct list_head	list;
> > +	struct notifier_block	*nb;
> > +	void			*token;
> > +	struct ioasid_set	*set;
> > +	bool			active;
> > +};
> > +
> >  enum ioasid_state {
> >  	IOASID_STATE_INACTIVE,
> >  	IOASID_STATE_ACTIVE,
> > @@ -394,6 +421,7 @@ EXPORT_SYMBOL_GPL(ioasid_find_by_spid);
> >  ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min,
> > ioasid_t max, void *private)
> >  {
> > +	struct ioasid_nb_args args;
> >  	struct ioasid_data *data;
> >  	void *adata;
> >  	ioasid_t id = INVALID_IOASID;
> > @@ -445,8 +473,14 @@ ioasid_t ioasid_alloc(struct ioasid_set *set,
> > ioasid_t min, ioasid_t max, goto exit_free;
> >  	}
> >  	set->nr_ioasids++;
> > -	goto done_unlock;
> > +	args.id = id;
> > +	/* Set private ID is not attached during allocation */
> > +	args.spid = INVALID_IOASID;
> > +	args.set = set;
> > +	atomic_notifier_call_chain(&set->nh, IOASID_ALLOC, &args);
> >  
> > +	spin_unlock(&ioasid_allocator_lock);
> > +	return id;  
> spurious change
Good catch. should just goto done_unlock.

> >  exit_free:
> >  	kfree(data);
> >  done_unlock:
> > @@ -479,6 +513,7 @@ static void ioasid_do_free(struct ioasid_data
> > *data) 
> >  static void ioasid_free_locked(struct ioasid_set *set, ioasid_t
> > ioasid) {
> > +	struct ioasid_nb_args args;
> >  	struct ioasid_data *data;
> >  
> >  	data = xa_load(&active_allocator->xa, ioasid);
> > @@ -491,7 +526,16 @@ static void ioasid_free_locked(struct
> > ioasid_set *set, ioasid_t ioasid) pr_warn("Cannot free IOASID %u
> > due to set ownership\n", ioasid); return;
> >  	}
> > +  
> spurious new line
got it

> >  	data->state = IOASID_STATE_FREE_PENDING;
> > +	/* Notify all users that this IOASID is being freed */
> > +	args.id = ioasid;
> > +	args.spid = data->spid;
> > +	args.pdata = data->private;
> > +	args.set = data->set;
> > +	atomic_notifier_call_chain(&ioasid_chain, IOASID_FREE,
> > &args);
> > +	/* Notify the ioasid_set for per set users */
> > +	atomic_notifier_call_chain(&set->nh, IOASID_FREE, &args);
> >  
> >  	if (!refcount_dec_and_test(&data->users))
> >  		return;  
> Shouldn't we call the notifier only when ref count == 0?
Not in the current scheme. The idea is to notify all users the PASID is
being freed, then each user can drop its reference. When refcount == 0,
the PASID will be returned to the pool.

> > @@ -514,6 +558,28 @@ void ioasid_free(struct ioasid_set *set,
> > ioasid_t ioasid) }
> >  EXPORT_SYMBOL_GPL(ioasid_free);
> >  
> > +static void ioasid_add_pending_nb(struct ioasid_set *set)
> > +{
> > +	struct ioasid_set_nb *curr;
> > +
> > +	if (set->type != IOASID_SET_TYPE_MM)
> > +		return;
> > +
> > +	/*
> > +	 * Check if there are any pending nb requests for the
> > given token, if so
> > +	 * add them to the notifier chain.
> > +	 */
> > +	spin_lock(&ioasid_nb_lock);
> > +	list_for_each_entry(curr, &ioasid_nb_pending_list, list) {
> > +		if (curr->token == set->token && !curr->active) {
> > +			atomic_notifier_chain_register(&set->nh,
> > curr->nb);
> > +			curr->set = set;
> > +			curr->active = true;
> > +		}
> > +	}
> > +	spin_unlock(&ioasid_nb_lock);
> > +}
> > +
> >  /**
> >   * ioasid_alloc_set - Allocate a new IOASID set for a given token
> >   *
> > @@ -601,6 +667,13 @@ struct ioasid_set *ioasid_alloc_set(void
> > *token, ioasid_t quota, int type) sdata->quota = quota;
> >  	sdata->sid = id;
> >  	refcount_set(&sdata->ref, 1);
> > +	ATOMIC_INIT_NOTIFIER_HEAD(&sdata->nh);
> > +
> > +	/*
> > +	 * Check if there are any pending nb requests for the
> > given token, if so
> > +	 * add them to the notifier chain.
> > +	 */
> > +	ioasid_add_pending_nb(sdata);
> >  
> >  	/*
> >  	 * Per set XA is used to store private IDs within the set,
> > get ready @@ -617,6 +690,30 @@ struct ioasid_set
> > *ioasid_alloc_set(void *token, ioasid_t quota, int type) }
> >  EXPORT_SYMBOL_GPL(ioasid_alloc_set);
> >  
> > +
> > +/*
> > + * ioasid_find_mm_set - Retrieve IOASID set with mm token
> > + * Take a reference of the set if found.
> > + */
> > +static struct ioasid_set *ioasid_find_mm_set(struct mm_struct
> > *token) +{
> > +	struct ioasid_set *sdata, *set = NULL;
> > +	unsigned long index;
> > +
> > +	spin_lock(&ioasid_allocator_lock);
> > +
> > +	xa_for_each(&ioasid_sets, index, sdata) {
> > +		if (sdata->type == IOASID_SET_TYPE_MM &&
> > sdata->token == token) {
> > +			refcount_inc(&sdata->ref);
> > +			set = sdata;
> > +			goto exit_unlock;
> > +		}
> > +	}
> > +exit_unlock:
> > +	spin_unlock(&ioasid_allocator_lock);
> > +	return set;
> > +}
> > +
> >  void ioasid_set_get_locked(struct ioasid_set *set)
> >  {
> >  	if (WARN_ON(xa_load(&ioasid_sets, set->sid) != set)) {
> > @@ -638,6 +735,8 @@ EXPORT_SYMBOL_GPL(ioasid_set_get);
> >  
> >  void ioasid_set_put_locked(struct ioasid_set *set)
> >  {
> > +	struct ioasid_nb_args args = { 0 };
> > +	struct ioasid_set_nb *curr;
> >  	struct ioasid_data *entry;
> >  	unsigned long index;
> >  
> > @@ -673,8 +772,24 @@ void ioasid_set_put_locked(struct ioasid_set
> > *set) done_destroy:
> >  	/* Return the quota back to system pool */
> >  	ioasid_capacity_avail += set->quota;
> > -	kfree_rcu(set, rcu);
> >  
> > +	/* Restore pending status of the set NBs */
> > +	spin_lock(&ioasid_nb_lock);
> > +	list_for_each_entry(curr, &ioasid_nb_pending_list, list) {
> > +		if (curr->token == set->token) {
> > +			if (curr->active)
> > +				curr->active = false;
> > +			else
> > +				pr_warn("Set token exists but not
> > active!\n");
> > +		}
> > +	}
> > +	spin_unlock(&ioasid_nb_lock);
> > +
> > +	args.set = set;
> > +	atomic_notifier_call_chain(&ioasid_chain, IOASID_SET_FREE,
> > &args); +
> > +	kfree_rcu(set, rcu);
> > +	pr_debug("Set freed %d\n", set->sid);
> >  	/*
> >  	 * Token got released right away after the ioasid_set is
> > freed.
> >  	 * If a new set is created immediately with the newly
> > released token, @@ -927,6 +1042,167 @@ void *ioasid_find(struct
> > ioasid_set *set, ioasid_t ioasid, }
> >  EXPORT_SYMBOL_GPL(ioasid_find);
> >  
> > +int ioasid_register_notifier(struct ioasid_set *set, struct
> > notifier_block *nb) +{
> > +	if (set)
> > +		return atomic_notifier_chain_register(&set->nh,
> > nb);
> > +	else
> > +		return
> > atomic_notifier_chain_register(&ioasid_chain, nb); +}
> > +EXPORT_SYMBOL_GPL(ioasid_register_notifier);
> > +
> > +void ioasid_unregister_notifier(struct ioasid_set *set,
> > +				struct notifier_block *nb)
> > +{
> > +	struct ioasid_set_nb *curr;
> > +
> > +	spin_lock(&ioasid_nb_lock);
> > +	/*
> > +	 * Pending list is registered with a token without an
> > ioasid_set,
> > +	 * therefore should not be unregistered directly.
> > +	 */
> > +	list_for_each_entry(curr, &ioasid_nb_pending_list, list) {
> > +		if (curr->nb == nb) {
> > +			pr_warn("Cannot unregister NB from pending
> > list\n");
> > +			spin_unlock(&ioasid_nb_lock);
> > +			return;
> > +		}
> > +	}
> > +	spin_unlock(&ioasid_nb_lock);  
> is it safe to release the lock here? What does prevent another NB to
> be added to ioasid_nb_pending_list after that?
Another NB will not be the same one as this NB, which is being removed.
I don't see any issues.
The only reason we check the pending list is to make sure the NB on the
pending list must be removed by ioasid_unregister_notifier_mm() API.

> > +
> > +	if (set)
> > +		atomic_notifier_chain_unregister(&set->nh, nb);
> > +	else
> > +		atomic_notifier_chain_unregister(&ioasid_chain,
> > nb); +}
> > +EXPORT_SYMBOL_GPL(ioasid_unregister_notifier);
> > +
> > +int ioasid_register_notifier_mm(struct mm_struct *mm, struct
> > notifier_block *nb) +{
> > +	struct ioasid_set_nb *curr;
> > +	struct ioasid_set *set;
> > +	int ret = 0;
> > +
> > +	if (!mm)
> > +		return -EINVAL;
> > +
> > +	spin_lock(&ioasid_nb_lock);
> > +
> > +	/* Check for duplicates, nb is unique per set */
> > +	list_for_each_entry(curr, &ioasid_nb_pending_list, list) {
> > +		if (curr->token == mm && curr->nb == nb) {
> > +			ret = -EBUSY;
> > +			goto exit_unlock;
> > +		}
> > +	}
> > +
> > +	/* Check if the token has an existing set */
> > +	set = ioasid_find_mm_set(mm);
> > +	if (IS_ERR_OR_NULL(set)) {
> > +		/* Add to the rsvd list as inactive */
> > +		curr->active = false;
> > +	} else {
> > +		/* REVISIT: Only register empty set for now. Can
> > add an option
> > +		 * in the future to playback existing PASIDs.
> > +		 */
> > +		if (set->nr_ioasids) {
> > +			pr_warn("IOASID set %d not empty\n",
> > set->sid);
> > +			ret = -EBUSY;
> > +			goto exit_unlock;
> > +		}
> > +		curr = kzalloc(sizeof(*curr), GFP_ATOMIC);
> > +		if (!curr) {
> > +			ret = -ENOMEM;
> > +			goto exit_unlock;
> > +		}
> > +		curr->token = mm;
> > +		curr->nb = nb;
> > +		curr->active = true;
> > +		curr->set = set;
> > +
> > +		/* Set already created, add to the notifier chain
> > */
> > +		atomic_notifier_chain_register(&set->nh, nb);
> > +		/*
> > +		 * Do not hold a reference, if the set gets
> > destroyed, the nb
> > +		 * entry will be marked inactive.
> > +		 */
> > +		ioasid_set_put(set);
> > +	}
> > +
> > +	list_add(&curr->list, &ioasid_nb_pending_list);
> > +
> > +exit_unlock:
> > +	spin_unlock(&ioasid_nb_lock);
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(ioasid_register_notifier_mm);
> > +
> > +void ioasid_unregister_notifier_mm(struct mm_struct *mm, struct
> > notifier_block *nb) +{
> > +	struct ioasid_set_nb *curr;
> > +
> > +	spin_lock(&ioasid_nb_lock);
> > +	list_for_each_entry(curr, &ioasid_nb_pending_list, list) {
> > +		if (curr->token == mm && curr->nb == nb) {
> > +			list_del(&curr->list);
> > +			goto exit_free;
> > +		}
> > +	}
> > +	pr_warn("No ioasid set found for mm token %llx\n",
> > (u64)mm);
> > +	goto done_unlock;
> > +
> > +exit_free:
> > +	if (curr->active) {
> > +		pr_debug("mm set active, unregister %llx\n",
> > +			(u64)mm);
> > +		atomic_notifier_chain_unregister(&curr->set->nh,
> > nb);
> > +	}
> > +	kfree(curr);
> > +done_unlock:
> > +	spin_unlock(&ioasid_nb_lock);
> > +	return;
> > +}
> > +EXPORT_SYMBOL_GPL(ioasid_unregister_notifier_mm);
> > +
> > +/**
> > + * 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
> > + * @flags:	Special instructions, e.g. notify with a set or
> > global
> > + */
> > +int ioasid_notify(ioasid_t ioasid, enum ioasid_notify_val cmd,
> > unsigned int flags) +{
> > +	struct ioasid_data *ioasid_data;
> > +	struct ioasid_nb_args args = { 0 };
> > +	int ret = 0;
> > +
> > +	spin_lock(&ioasid_allocator_lock);
> > +	ioasid_data = xa_load(&active_allocator->xa, ioasid);
> > +	if (!ioasid_data) {
> > +		pr_err("Trying to notify unknown IOASID %u\n",
> > ioasid);
> > +		spin_unlock(&ioasid_allocator_lock);
> > +		return -EINVAL;
> > +	}
> > +
> > +	args.id = ioasid;
> > +	args.set = ioasid_data->set;
> > +	args.pdata = ioasid_data->private;
> > +	args.spid = ioasid_data->spid;
> > +	if (flags & IOASID_NOTIFY_ALL) {
> > +		ret = atomic_notifier_call_chain(&ioasid_chain,
> > cmd, &args);
> > +	} else if (flags & IOASID_NOTIFY_SET) {
> > +		ret =
> > atomic_notifier_call_chain(&ioasid_data->set->nh,
> > +						 cmd, &args);
> > +	}
> > +	spin_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 d4b3e83672f6..572111cd3b4b 100644
> > --- a/include/linux/ioasid.h
> > +++ b/include/linux/ioasid.h
> > @@ -23,6 +23,7 @@ enum ioasid_set_type {
> >   * struct ioasid_set - Meta data about ioasid_set
> >   * @type:	Token types and other features
> >   * @token:	Unique to identify an IOASID set
> > + * @nh:		Notifier for IOASID events within the set  
> list of notifiers private to that set?
Sounds more accurate.

> >   * @xa:		XArray to store ioasid_set private IDs, can
> > be used for
> >   *		guest-host IOASID mapping, or just a private
> > IOASID namespace.
> >   * @quota:	Max number of IOASIDs can be allocated within
> > the set @@ -32,6 +33,7 @@ enum ioasid_set_type {
> >   */
> >  struct ioasid_set {
> >  	void *token;
> > +	struct atomic_notifier_head nh;
> >  	struct xarray xa;
> >  	int type;
> >  	int quota;
> > @@ -56,6 +58,49 @@ 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,
> > +	IOASID_SET_ALLOC,
> > +	IOASID_SET_FREE,
> > +};
> > +
> > +#define IOASID_NOTIFY_ALL BIT(0)
> > +#define IOASID_NOTIFY_SET BIT(1)
> > +/**
> > + * enum ioasid_notifier_prios - IOASID event notification order
> > + *
> > + * When status of an IOASID changes, users might need to take
> > actions to
> > + * reflect the new state. For example, when an IOASID is freed due
> > to
> > + * exception, the hardware context in virtual CPU, DMA device, and
> > IOMMU
> > + * shall be cleared and drained. Order is required to prevent life
> > cycle
> > + * problems.
> > + */
> > +enum ioasid_notifier_prios {
> > +	IOASID_PRIO_LAST,
> > +	IOASID_PRIO_DEVICE,
> > +	IOASID_PRIO_IOMMU,
> > +	IOASID_PRIO_CPU,
> > +};
> > +
> > +/**
> > + * struct ioasid_nb_args - Argument provided by IOASID core when
> > notifier
> > + * is called.
> > + * @id:		The IOASID being notified
> > + * @spid:	The set private ID associated with the IOASID
> > + * @set:	The IOASID set of @id
> > + * @pdata:	The private data attached to the IOASID
> > + */
> > +struct ioasid_nb_args {
> > +	ioasid_t id;
> > +	ioasid_t spid;
> > +	struct ioasid_set *set;
> > +	void *pdata;
> > +};
> > +
> >  #if IS_ENABLED(CONFIG_IOASID)
> >  void ioasid_install_capacity(ioasid_t total);
> >  ioasid_t ioasid_get_capacity(void);
> > @@ -75,8 +120,16 @@ void *ioasid_find(struct ioasid_set *set,
> > ioasid_t ioasid, bool (*getter)(void * int
> > ioasid_attach_data(ioasid_t ioasid, void *data); int
> > ioasid_attach_spid(ioasid_t ioasid, ioasid_t spid); ioasid_t
> > ioasid_find_by_spid(struct ioasid_set *set, ioasid_t spid); +
> > +int ioasid_register_notifier(struct ioasid_set *set,
> > +			struct notifier_block *nb);
> > +void ioasid_unregister_notifier(struct ioasid_set *set,
> > +				struct notifier_block *nb);
> > +
> >  int ioasid_register_allocator(struct ioasid_allocator_ops
> > *allocator); void ioasid_unregister_allocator(struct
> > ioasid_allocator_ops *allocator); +
> > +int ioasid_notify(ioasid_t ioasid, enum ioasid_notify_val cmd,
> > unsigned int flags); void ioasid_is_in_set(struct ioasid_set *set,
> > ioasid_t ioasid); int ioasid_get(struct ioasid_set *set, ioasid_t
> > ioasid); int ioasid_get_locked(struct ioasid_set *set, ioasid_t
> > ioasid); @@ -85,6 +138,9 @@ void ioasid_put_locked(struct
> > ioasid_set *set, ioasid_t ioasid); int
> > ioasid_set_for_each_ioasid(struct ioasid_set *sdata, void
> > (*fn)(ioasid_t id, void *data), void *data);
> > +int ioasid_register_notifier_mm(struct mm_struct *mm, struct
> > notifier_block *nb); +void ioasid_unregister_notifier_mm(struct
> > mm_struct *mm, struct notifier_block *nb); +
> >  #else /* !CONFIG_IOASID */
> >  static inline void ioasid_install_capacity(ioasid_t total)
> >  {
> > @@ -124,6 +180,20 @@ static inline void *ioasid_find(struct
> > ioasid_set *set, ioasid_t ioasid, bool (* return NULL;
> >  }
> >  
> > +static inline int ioasid_register_notifier(struct notifier_block
> > *nb) +{
> > +	return -ENOTSUPP;
> > +}
> > +
> > +static inline void ioasid_unregister_notifier(struct
> > notifier_block *nb) +{
> > +}
> > +
> > +static inline int ioasid_notify(ioasid_t ioasid, enum
> > ioasid_notify_val cmd, unsigned int flags) +{
> > +	return -ENOTSUPP;
> > +}
> > +
> >  static inline int ioasid_register_allocator(struct
> > ioasid_allocator_ops *allocator) {
> >  	return -ENOTSUPP;
> >   
> Thanks
> 
> Eric
> 
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[Jacob Pan]