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Date:   Wed, 21 Oct 2020 16:55:53 +0200
From:   Jean-Philippe Brucker <jean-philippe@linaro.org>
To:     Jacob Pan <jacob.pan.linux@gmail.com>
Cc:     iommu@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Jonathan Corbet <corbet@lwn.net>, linux-api@vger.kernel.org,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Eric Auger <eric.auger@redhat.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Yi Liu <yi.l.liu@intel.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Raj Ashok <ashok.raj@intel.com>, Wu Hao <hao.wu@intel.com>,
        Yi Sun <yi.y.sun@intel.com>, Dave Jiang <dave.jiang@intel.com>,
        Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v3 05/14] iommu/ioasid: Redefine IOASID set and
 allocation APIs
Message-ID: <20201021145553.GC1653231@myrica>
References: <1601329121-36979-1-git-send-email-jacob.jun.pan@linux.intel.com>
 <1601329121-36979-6-git-send-email-jacob.jun.pan@linux.intel.com>
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In-Reply-To: <1601329121-36979-6-git-send-email-jacob.jun.pan@linux.intel.com>
Precedence: bulk

On Mon, Sep 28, 2020 at 02:38:32PM -0700, Jacob Pan wrote:
> ioasid_set was introduced as an arbitrary token that is shared by a
> group of IOASIDs. For example, two IOASIDs allocated via the same
> ioasid_set pointer belong to the same set.
> 
> For guest SVA usages, system-wide IOASID resources need to be
> partitioned such that each VM can have its own quota and being managed
> separately. ioasid_set is the perfect candidate for meeting such
> requirements. This patch redefines and extends ioasid_set with the
> following new fields:
> - Quota
> - Reference count
> - Storage of its namespace
> - The token is now stored in the ioasid_set with types
> 
> Basic ioasid_set level APIs are introduced that wire up these new data.
> Existing users of IOASID APIs are converted where a host IOASID set is
> allocated for bare-metal usage.
> 
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
>  drivers/iommu/intel/iommu.c |  26 +++--
>  drivers/iommu/intel/pasid.h |   1 +
>  drivers/iommu/intel/svm.c   |  25 ++--
>  drivers/iommu/ioasid.c      | 277 ++++++++++++++++++++++++++++++++++++++++----
>  include/linux/ioasid.h      |  53 +++++++--
>  5 files changed, 333 insertions(+), 49 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index e7bcb299e51e..872391890323 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -104,6 +104,9 @@
>   */
>  #define INTEL_IOMMU_PGSIZES	(~0xFFFUL)
>  
> +/* PASIDs used by host SVM */
> +struct ioasid_set *host_pasid_set;
> +
>  static inline int agaw_to_level(int agaw)
>  {
>  	return agaw + 2;
> @@ -3147,8 +3150,8 @@ static void intel_vcmd_ioasid_free(ioasid_t ioasid, void *data)
>  	 * Sanity check the ioasid owner is done at upper layer, e.g. VFIO
>  	 * We can only free the PASID when all the devices are unbound.
>  	 */
> -	if (ioasid_find(NULL, ioasid, NULL)) {
> -		pr_alert("Cannot free active IOASID %d\n", ioasid);
> +	if (IS_ERR(ioasid_find(host_pasid_set, ioasid, NULL))) {
> +		pr_err("IOASID %d to be freed but not in system set\n", ioasid);
>  		return;
>  	}
>  	vcmd_free_pasid(iommu, ioasid);
> @@ -3333,8 +3336,17 @@ static int __init init_dmars(void)
>  		goto free_iommu;
>  
>  	/* PASID is needed for scalable mode irrespective to SVM */
> -	if (intel_iommu_sm)
> +	if (intel_iommu_sm) {
>  		ioasid_install_capacity(intel_pasid_max_id);
> +		/* We should not run out of IOASIDs at boot */
> +		host_pasid_set = ioasid_set_alloc(NULL, PID_MAX_DEFAULT,
> +						  IOASID_SET_TYPE_NULL);
> +		if (IS_ERR_OR_NULL(host_pasid_set)) {
> +			pr_err("Failed to allocate host PASID set %lu\n",

Printing a negative value as unsigned

> +				PTR_ERR(host_pasid_set));
> +			intel_iommu_sm = 0;
> +		}
> +	}
>  
>  	/*
>  	 * for each drhd
> @@ -3381,7 +3393,7 @@ static int __init init_dmars(void)
>  		disable_dmar_iommu(iommu);
>  		free_dmar_iommu(iommu);
>  	}
> -
> +	ioasid_set_put(host_pasid_set);
>  	kfree(g_iommus);
>  
>  error:
> @@ -5163,7 +5175,7 @@ static void auxiliary_unlink_device(struct dmar_domain *domain,
>  	domain->auxd_refcnt--;
>  
>  	if (!domain->auxd_refcnt && domain->default_pasid > 0)
> -		ioasid_free(domain->default_pasid);
> +		ioasid_free(host_pasid_set, domain->default_pasid);
>  }
>  
>  static int aux_domain_add_dev(struct dmar_domain *domain,
> @@ -5181,7 +5193,7 @@ static int aux_domain_add_dev(struct dmar_domain *domain,
>  		int pasid;
>  
>  		/* No private data needed for the default pasid */
> -		pasid = ioasid_alloc(NULL, PASID_MIN,
> +		pasid = ioasid_alloc(host_pasid_set, PASID_MIN,
>  				     pci_max_pasids(to_pci_dev(dev)) - 1,
>  				     NULL);
>  		if (pasid == INVALID_IOASID) {
> @@ -5224,7 +5236,7 @@ static int aux_domain_add_dev(struct dmar_domain *domain,
>  	spin_unlock(&iommu->lock);
>  	spin_unlock_irqrestore(&device_domain_lock, flags);
>  	if (!domain->auxd_refcnt && domain->default_pasid > 0)
> -		ioasid_free(domain->default_pasid);
> +		ioasid_free(host_pasid_set, domain->default_pasid);
>  
>  	return ret;
>  }
> diff --git a/drivers/iommu/intel/pasid.h b/drivers/iommu/intel/pasid.h
> index c9850766c3a9..ccdc23446015 100644
> --- a/drivers/iommu/intel/pasid.h
> +++ b/drivers/iommu/intel/pasid.h
> @@ -99,6 +99,7 @@ static inline bool pasid_pte_is_present(struct pasid_entry *pte)
>  }
>  
>  extern u32 intel_pasid_max_id;
> +extern struct ioasid_set *host_pasid_set;
>  int intel_pasid_alloc_id(void *ptr, int start, int end, gfp_t gfp);
>  void intel_pasid_free_id(int pasid);
>  void *intel_pasid_lookup_id(int pasid);
> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
> index 06a16bee7b65..2e764e283469 100644
> --- a/drivers/iommu/intel/svm.c
> +++ b/drivers/iommu/intel/svm.c
> @@ -228,7 +228,9 @@ static LIST_HEAD(global_svm_list);
>  	list_for_each_entry((sdev), &(svm)->devs, list)	\
>  		if ((d) != (sdev)->dev) {} else
>  
> -static int pasid_to_svm_sdev(struct device *dev, unsigned int pasid,
> +static int pasid_to_svm_sdev(struct device *dev,
> +			     struct ioasid_set *set,
> +			     unsigned int pasid,
>  			     struct intel_svm **rsvm,
>  			     struct intel_svm_dev **rsdev)
>  {
> @@ -242,7 +244,7 @@ static int pasid_to_svm_sdev(struct device *dev, unsigned int pasid,
>  	if (pasid == INVALID_IOASID || pasid >= PASID_MAX)
>  		return -EINVAL;
>  
> -	svm = ioasid_find(NULL, pasid, NULL);
> +	svm = ioasid_find(set, pasid, NULL);
>  	if (IS_ERR(svm))
>  		return PTR_ERR(svm);
>  
> @@ -312,7 +314,8 @@ int intel_svm_bind_gpasid(struct iommu_domain *domain, struct device *dev,
>  	dmar_domain = to_dmar_domain(domain);
>  
>  	mutex_lock(&pasid_mutex);
> -	ret = pasid_to_svm_sdev(dev, data->hpasid, &svm, &sdev);
> +	ret = pasid_to_svm_sdev(dev, NULL,
> +				data->hpasid, &svm, &sdev);
>  	if (ret)
>  		goto out;
>  
> @@ -417,7 +420,7 @@ int intel_svm_unbind_gpasid(struct device *dev, int pasid)
>  		return -EINVAL;
>  
>  	mutex_lock(&pasid_mutex);
> -	ret = pasid_to_svm_sdev(dev, pasid, &svm, &sdev);
> +	ret = pasid_to_svm_sdev(dev, NULL, pasid, &svm, &sdev);
>  	if (ret)
>  		goto out;
>  
> @@ -555,7 +558,7 @@ intel_svm_bind_mm(struct device *dev, int flags, struct svm_dev_ops *ops,
>  			pasid_max = intel_pasid_max_id;
>  
>  		/* Do not use PASID 0, reserved for RID to PASID */
> -		svm->pasid = ioasid_alloc(NULL, PASID_MIN,
> +		svm->pasid = ioasid_alloc(host_pasid_set, PASID_MIN,
>  					  pasid_max - 1, svm);
>  		if (svm->pasid == INVALID_IOASID) {
>  			kfree(svm);
> @@ -572,7 +575,7 @@ intel_svm_bind_mm(struct device *dev, int flags, struct svm_dev_ops *ops,
>  		if (mm) {
>  			ret = mmu_notifier_register(&svm->notifier, mm);
>  			if (ret) {
> -				ioasid_free(svm->pasid);
> +				ioasid_free(host_pasid_set, svm->pasid);
>  				kfree(svm);
>  				kfree(sdev);
>  				goto out;
> @@ -590,7 +593,7 @@ intel_svm_bind_mm(struct device *dev, int flags, struct svm_dev_ops *ops,
>  		if (ret) {
>  			if (mm)
>  				mmu_notifier_unregister(&svm->notifier, mm);
> -			ioasid_free(svm->pasid);
> +			ioasid_free(host_pasid_set, svm->pasid);
>  			kfree(svm);
>  			kfree(sdev);
>  			goto out;
> @@ -638,7 +641,8 @@ static int intel_svm_unbind_mm(struct device *dev, int pasid)
>  	if (!iommu)
>  		goto out;
>  
> -	ret = pasid_to_svm_sdev(dev, pasid, &svm, &sdev);
> +	ret = pasid_to_svm_sdev(dev, host_pasid_set,
> +				pasid, &svm, &sdev);
>  	if (ret)
>  		goto out;
>  
> @@ -659,7 +663,7 @@ static int intel_svm_unbind_mm(struct device *dev, int pasid)
>  			kfree_rcu(sdev, rcu);
>  
>  			if (list_empty(&svm->devs)) {
> -				ioasid_free(svm->pasid);
> +				ioasid_free(host_pasid_set, svm->pasid);
>  				if (svm->mm)
>  					mmu_notifier_unregister(&svm->notifier, svm->mm);
>  				list_del(&svm->list);
> @@ -1130,7 +1134,8 @@ int intel_svm_page_response(struct device *dev,
>  		goto out;
>  	}
>  
> -	ret = pasid_to_svm_sdev(dev, prm->pasid, &svm, &sdev);
> +	ret = pasid_to_svm_sdev(dev, host_pasid_set,
> +				prm->pasid, &svm, &sdev);
>  	if (ret || !sdev) {
>  		ret = -ENODEV;
>  		goto out;
> diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
> index 4277cb17e15b..61e25c2375ab 100644
> --- a/drivers/iommu/ioasid.c
> +++ b/drivers/iommu/ioasid.c
> @@ -1,8 +1,8 @@
>  // SPDX-License-Identifier: GPL-2.0
>  /*
>   * I/O Address Space ID allocator. There is one global IOASID space, split into
> - * subsets. Users create a subset with DECLARE_IOASID_SET, then allocate and
> - * free IOASIDs with ioasid_alloc and ioasid_free.
> + * sets. Users create a set with ioasid_set_alloc, then allocate/free IDs
> + * with ioasid_alloc and ioasid_free.
>   */
>  #include <linux/ioasid.h>
>  #include <linux/module.h>
> @@ -14,6 +14,8 @@
>  #define PCI_PASID_MAX 0x100000
>  static ioasid_t ioasid_capacity = PCI_PASID_MAX;
>  static ioasid_t ioasid_capacity_avail = PCI_PASID_MAX;
> +static DEFINE_XARRAY_ALLOC(ioasid_sets);
> +
>  struct ioasid_data {
>  	ioasid_t id;
>  	struct ioasid_set *set;
> @@ -343,6 +345,114 @@ void ioasid_detach_data(ioasid_t ioasid)
>  }
>  EXPORT_SYMBOL_GPL(ioasid_detach_data);
>  
> +static inline bool ioasid_set_is_valid(struct ioasid_set *set)

'inline' isn't needed

> +{
> +	return xa_load(&ioasid_sets, set->id) == set;
> +}
> +
> +/**
> + * ioasid_set_alloc - Allocate a new IOASID set for a given token
> + *
> + * @token:	An optional arbitrary number that can be associated with the
> + *		IOASID set. @token can be NULL if the type is
> + *		IOASID_SET_TYPE_NULL
> + * @quota:	Quota allowed in this set
> + * @type:	The type of the token used to create the IOASID set
> + *
> + * IOASID is limited system-wide resource that requires quota management.
> + * Token will be stored in the ioasid_set returned. A reference will be taken
> + * on the newly created set. Subsequent IOASID allocation within the set need
> + * to use the retured ioasid_set pointer.

                 returned

> + */
> +struct ioasid_set *ioasid_set_alloc(void *token, ioasid_t quota, int type)
> +{
> +	struct ioasid_set *set;
> +	unsigned long index;
> +	ioasid_t id;
> +
> +	if (type >= IOASID_SET_TYPE_NR)
> +		return ERR_PTR(-EINVAL);
> +
> +	/* REVISIT: may support set w/o quota, use system available */

You can drop this comment, anyone wanting to pass a quota of zero can send
a patch.

> +	if (!quota)
> +		return ERR_PTR(-EINVAL);
> +
> +	/*
> +	 * Need to check space available if we share system-wide quota.
> +	 * TODO: we may need to support quota free sets in the future.

You can drop this too

> +	 */
> +	spin_lock(&ioasid_allocator_lock);
> +	if (quota > ioasid_capacity_avail) {
> +		pr_warn("Out of IOASID capacity! ask %d, avail %d\n",
> +			quota, ioasid_capacity_avail);
> +		set = ERR_PTR(-ENOSPC);
> +		goto exit_unlock;
> +	}
> +
> +	/*
> +	 * Token is only unique within its types but right now we have only
> +	 * mm type. If we have more token types, we have to match type as well.
> +	 */
> +	switch (type) {
> +	case IOASID_SET_TYPE_MM:
> +		if (!token) {
> +			set = ERR_PTR(-EINVAL);
> +			goto exit_unlock;
> +		}
> +		/* Search existing set tokens, reject duplicates */
> +		xa_for_each(&ioasid_sets, index, set) {
> +			if (set->token == token &&
> +				set->type == IOASID_SET_TYPE_MM) {

misaligned

> +				set = ERR_PTR(-EEXIST);
> +				goto exit_unlock;
> +			}
> +		}
> +		break;
> +	case IOASID_SET_TYPE_NULL:
> +		if (!token)
> +			break;
> +		fallthrough;
> +	default:
> +		pr_err("Invalid token and IOASID type\n");
> +		set = ERR_PTR(-EINVAL);
> +		goto exit_unlock;
> +	}
> +
> +	set = kzalloc(sizeof(*set), GFP_ATOMIC);
> +	if (!set) {
> +		set = ERR_PTR(-ENOMEM);
> +		goto exit_unlock;
> +	}
> +
> +	if (xa_alloc(&ioasid_sets, &id, set,
> +		     XA_LIMIT(0, ioasid_capacity_avail - quota),
> +		     GFP_ATOMIC)) {
> +		kfree(set);
> +		set = ERR_PTR(-ENOSPC);
> +		goto exit_unlock;
> +	}
> +
> +	set->token = token;
> +	set->type = type;
> +	set->quota = quota;
> +	set->id = id;
> +	refcount_set(&set->ref, 1);
> +
> +	/*
> +	 * Per set XA is used to store private IDs within the set, get ready

Could drop "get ready". But I think the comment on the ioasid_set struct
is sufficient, maybe you can drop this whole comment.

> +	 * for ioasid_set private ID and system-wide IOASID allocation
> +	 * results.
> +	 */
> +	xa_init(&set->xa);
> +	ioasid_capacity_avail -= quota;
> +
> +exit_unlock:
> +	spin_unlock(&ioasid_allocator_lock);
> +
> +	return set;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_set_alloc);
> +
>  /**
>   * ioasid_alloc - Allocate an IOASID
>   * @set: the IOASID set
> @@ -360,11 +470,22 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
>  {
>  	struct ioasid_data *data;
>  	void *adata;
> -	ioasid_t id;
> +	ioasid_t id = INVALID_IOASID;
> +
> +	spin_lock(&ioasid_allocator_lock);
> +	/* Check if the IOASID set has been allocated and initialized */
> +	if (WARN_ON(!ioasid_set_is_valid(set)))
> +		goto done_unlock;
> +
> +	if (set->quota <= set->nr_ioasids) {
> +		pr_err_ratelimited("IOASID set out of quota %d\n",
> +				   set->quota);
> +		goto done_unlock;
> +	}
>  
>  	data = kzalloc(sizeof(*data), GFP_ATOMIC);
>  	if (!data)
> -		return INVALID_IOASID;
> +		goto done_unlock;
>  
>  	data->set = set;
>  	data->private = private;
> @@ -373,11 +494,10 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
>  	 * Custom allocator needs allocator data to perform platform specific
>  	 * operations.
>  	 */
> -	spin_lock(&ioasid_allocator_lock);
>  	adata = active_allocator->flags & IOASID_ALLOCATOR_CUSTOM ? active_allocator->ops->pdata : data;
>  	id = active_allocator->ops->alloc(min, max, adata);
>  	if (id == INVALID_IOASID) {
> -		pr_err("Failed ASID allocation %lu\n", active_allocator->flags);
> +		pr_err_ratelimited("Failed IOASID allocation %lu\n", active_allocator->flags);
>  		goto exit_free;
>  	}
>  
> @@ -386,46 +506,153 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
>  		/* Custom allocator needs framework to store and track allocation results */
>  		pr_err("Failed to alloc ioasid from %d\n", id);
>  		active_allocator->ops->free(id, active_allocator->ops->pdata);
> +		if (active_allocator->flags & IOASID_ALLOCATOR_CUSTOM)
> +			xa_erase(&active_allocator->xa, id);

That doesn't look right, given we get here if the CUSTOM flag is set and
xa_alloc() fails. Should it be in the next block?

>  		goto exit_free;
>  	}
>  	data->id = id;
>  
> -	spin_unlock(&ioasid_allocator_lock);
> -	return id;
> +	/* Store IOASID in the per set data */
> +	if (xa_err(xa_store(&set->xa, id, data, GFP_ATOMIC))) {
> +		pr_err_ratelimited("Failed to store ioasid %d in set\n", id);
> +		active_allocator->ops->free(id, active_allocator->ops->pdata);
> +		goto exit_free;

Should set id = INVALID_IOASID. I feel this function would be more
readable if we keep separate error and success paths.

> +	}
> +	set->nr_ioasids++;
> +	goto done_unlock;
>  exit_free:
> -	spin_unlock(&ioasid_allocator_lock);
>  	kfree(data);
> -	return INVALID_IOASID;
> +done_unlock:
> +	spin_unlock(&ioasid_allocator_lock);
> +	return id;
>  }
>  EXPORT_SYMBOL_GPL(ioasid_alloc);
>  
> -/**
> - * ioasid_free - Free an IOASID
> - * @ioasid: the ID to remove
> - */
> -void ioasid_free(ioasid_t ioasid)
> +static void ioasid_do_free_locked(struct ioasid_data *data)
>  {
>  	struct ioasid_data *ioasid_data;
>  
> -	spin_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);
> -		goto exit_unlock;
> -	}
> -
> -	active_allocator->ops->free(ioasid, active_allocator->ops->pdata);
> +	active_allocator->ops->free(data->id, active_allocator->ops->pdata);
>  	/* Custom allocator needs additional steps to free the xa element */
>  	if (active_allocator->flags & IOASID_ALLOCATOR_CUSTOM) {
> -		ioasid_data = xa_erase(&active_allocator->xa, ioasid);
> +		ioasid_data = xa_erase(&active_allocator->xa, data->id);
>  		kfree_rcu(ioasid_data, rcu);
>  	}
>  
> -exit_unlock:
> +	data->set->nr_ioasids--;
> +	xa_erase(&data->set->xa, data->id);
> +}
> +
> +static void ioasid_free_locked(struct ioasid_set *set, ioasid_t ioasid)
> +{
> +	struct ioasid_data *data;
> +
> +	data = xa_load(&active_allocator->xa, ioasid);
> +	if (!data) {
> +		pr_err("Trying to free unknown IOASID %u\n", ioasid);
> +		return;
> +	}
> +	if (data->set != set) {
> +		pr_warn("Cannot free IOASID %u due to set ownership\n", ioasid);
> +		return;
> +	}
> +	/* Check if the set exists */
> +	if (WARN_ON(!xa_load(&ioasid_sets, data->set->id)))
> +		return;
> +
> +	ioasid_do_free_locked(data);
> +}
> +
> +/**
> + * ioasid_free - Drop reference on an IOASID. Free if refcount drops to 0,
> + *               including free from its set and system-wide list.
> + * @set:	The ioasid_set to check permission with. If not NULL, IOASID
> + *		free will fail if the set does not match.
> + * @ioasid:	The IOASID to remove
> + */
> +void ioasid_free(struct ioasid_set *set, ioasid_t ioasid)
> +{
> +	spin_lock(&ioasid_allocator_lock);
> +	ioasid_free_locked(set, ioasid);
>  	spin_unlock(&ioasid_allocator_lock);
>  }
>  EXPORT_SYMBOL_GPL(ioasid_free);
>  
> +static void ioasid_set_get_locked(struct ioasid_set *set)
> +{
> +	if (WARN_ON(!ioasid_set_is_valid(set)))
> +		return;
> +
> +	refcount_inc(&set->ref);
> +}
> +
> +void ioasid_set_get(struct ioasid_set *set)
> +{
> +	spin_lock(&ioasid_allocator_lock);
> +	ioasid_set_get_locked(set);
> +	spin_unlock(&ioasid_allocator_lock);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_set_get);
> +
> +static void ioasid_set_put_locked(struct ioasid_set *set)
> +{
> +	struct ioasid_data *entry;
> +	unsigned long index;
> +
> +	if (WARN_ON(!ioasid_set_is_valid(set)))
> +		return;
> +
> +	if (!refcount_dec_and_test(&set->ref))
> +		return;
> +
> +	/* The set is already empty, we just destroy the set. */
> +	if (xa_empty(&set->xa))
> +		goto done_destroy;

Do we need this optimization, if xa_for_each() is allowed on the empty xa?
This function doesn't really need to be fast. Otherwise you can just test
nr_ioasids.

> +
> +	/*
> +	 * Free all PASIDs from system-wide IOASID pool, all subscribers gets
> +	 * notified and do cleanup of their own.
> +	 * Note that some references of the IOASIDs within the set can still
> +	 * be held after the free call. This is OK in that the IOASIDs will be
> +	 * marked inactive, the only operations can be done is ioasid_put.
> +	 * No need to track IOASID set states since there is no reclaim phase.
> +	 */
> +	xa_for_each(&set->xa, index, entry) {
> +		ioasid_free_locked(set, index);
> +		/* Free from per set private pool */
> +		xa_erase(&set->xa, index);
> +	}
> +
> +done_destroy:
> +	/* Return the quota back to system pool */
> +	ioasid_capacity_avail += set->quota;
> +
> +	/*
> +	 * Token got released right away after the ioasid_set is freed.
> +	 * If a new set is created immediately with the newly released token,
> +	 * it will not allocate the same IOASIDs unless they are reclaimed.
> +	 */
> +	xa_erase(&ioasid_sets, set->id);
> +	kfree_rcu(set, rcu);
> +}
> +
> +/**
> + * ioasid_set_put - Drop a reference to the IOASID set. Free all IOASIDs within
> + *                  the set if there are no more users.
> + *
> + * @set:	The IOASID set ID to be freed
> + *
> + * If refcount drops to zero, all IOASIDs allocated within the set will be
> + * freed.
> + */
> +void ioasid_set_put(struct ioasid_set *set)
> +{
> +	spin_lock(&ioasid_allocator_lock);
> +	ioasid_set_put_locked(set);
> +	spin_unlock(&ioasid_allocator_lock);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_set_put);
> +
>  /**
>   * ioasid_find - Find IOASID data
>   * @set: the IOASID set
> diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
> index 7fc320656be2..1ae213b660f0 100644
> --- a/include/linux/ioasid.h
> +++ b/include/linux/ioasid.h
> @@ -4,14 +4,43 @@
>  
>  #include <linux/types.h>
>  #include <linux/errno.h>
> +#include <linux/xarray.h>
> +#include <linux/refcount.h>
>  
>  #define INVALID_IOASID ((ioasid_t)-1)
>  typedef unsigned int ioasid_t;
>  typedef ioasid_t (*ioasid_alloc_fn_t)(ioasid_t min, ioasid_t max, void *data);
>  typedef void (*ioasid_free_fn_t)(ioasid_t ioasid, void *data);
>  
> +/* IOASID set types */
> +enum ioasid_set_type {
> +	IOASID_SET_TYPE_NULL = 1, /* Set token is NULL */
> +	IOASID_SET_TYPE_MM,	  /* Set token is a mm_struct pointer
> +				   * i.e. associated with a process
> +				   */
> +	IOASID_SET_TYPE_NR,
> +};
> +
> +/**
> + * struct ioasid_set - Meta data about ioasid_set
> + * @xa:		XArray to store ioasid_set private IDs, can be used for
> + *		guest-host IOASID mapping, or just a private IOASID namespace.
> + * @token:	Unique to identify an IOASID set
> + * @type:	Token types
> + * @quota:	Max number of IOASIDs can be allocated within the set
> + * @nr_ioasids:	Number of IOASIDs currently allocated in the set
> + * @id:		ID of the set
> + * @ref:	Reference count of the users
> + */
>  struct ioasid_set {
> -	int dummy;
> +	struct xarray xa;
> +	void *token;
> +	int type;

Could be an 'enum ioasid_set_type'

> +	int quota;
> +	int nr_ioasids;

These could be unsigned, or ioasid_t

> +	int id;

unsigned as well

> +	refcount_t ref;
> +	struct rcu_head rcu;
>  };
>  
>  /**
> @@ -29,14 +58,16 @@ struct ioasid_allocator_ops {
>  	void *pdata;
>  };
>  
> -#define DECLARE_IOASID_SET(name) struct ioasid_set name = { 0 }
> -
>  #if IS_ENABLED(CONFIG_IOASID)
>  void ioasid_install_capacity(ioasid_t total);
>  ioasid_t ioasid_get_capacity(void);
> +struct ioasid_set *ioasid_set_alloc(void *token, ioasid_t quota, int type);
> +void ioasid_set_get(struct ioasid_set *set);
> +void ioasid_set_put(struct ioasid_set *set);
> +
>  ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
>  		      void *private);
> -void ioasid_free(ioasid_t ioasid);
> +void ioasid_free(struct ioasid_set *set, ioasid_t ioasid);
>  void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
>  		  bool (*getter)(void *));
>  int ioasid_register_allocator(struct ioasid_allocator_ops *allocator);
> @@ -59,12 +90,20 @@ static inline ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min,
>  	return INVALID_IOASID;
>  }
>  
> -static inline void ioasid_free(ioasid_t ioasid)
> +static inline void ioasid_free(struct ioasid_set *set, ioasid_t ioasid)
> +{
> +}
> +
> +static inline struct ioasid_set *ioasid_set_alloc(void *token, ioasid_t quota, int type)
> +{
> +	return ERR_PTR(-ENOTSUPP);
> +}
> +
> +static inline void ioasid_set_put(struct ioasid_set *set)
>  {
>  }

A stub is missing for ioasid_set_get()

>  
> -static inline void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
> -				bool (*getter)(void *))
> +static inline void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid, bool (*getter)(void *))

Spurious change?

Thanks,
Jean

>  {
>  	return NULL;
>  }
> -- 
> 2.7.4
>