Re: [PATCH v2 6/9] iommu/ioasid: Introduce notification APIs

From: Jean-Philippe Brucker
Date: Tue Aug 25 2020 - 06:26:38 EST

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On Fri, Aug 21, 2020 at 09:35:15PM -0700, 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@xxxxxxxxx>
> Signed-off-by: Wu Hao <hao.wu@xxxxxxxxx>
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
> 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

consumer

> + * hardware contexts associated with IOASIDs.
> + * When a status change occurs, such as IOASID is being freed, notifier chains
> + * 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.

The patch adds both

> + */
> +static ATOMIC_NOTIFIER_HEAD(ioasid_chain);

"ioasid_notifier" may be clearer

> +
> +/* 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;

args.pdata is uninitialized

> + atomic_notifier_call_chain(&set->nh, IOASID_ALLOC, &args);

No global notification?

>
> + spin_unlock(&ioasid_allocator_lock);
> + return id;
> 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;
> }
> +
> 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;
> @@ -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;

Or just break

> + }
> + }
> +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);

set might have been freed

> /*
> * 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)

Maybe add a bit of documentation on the difference with the _mm variant,
as well as the @set parameter.

Will this be used by anyone at first? We could introduce only the _mm
functions for now.

> +{
> + 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);
> +
> + 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);

Seems to be a deadlock here, as ioasid_find_mm_set() grabs
ioasid_allocator_lock while holding ioasid_nb_lock, and
ioasid_set_put/get_locked() grabs ioasid_nb_lock while holding
ioasid_allocator_lock.

> + if (IS_ERR_OR_NULL(set)) {

Looks a bit off, maybe we can check !set since ioasid_find_mm_set()
doesn't return errors.

> + /* Add to the rsvd list as inactive */
> + curr->active = false;

curr isn't valid here

> + } 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);

As a side-note, I think there's too much atomic allocation in this file,
I'd like to try and rework the locking once it stabilizes and I find some
time. Do you remember why ioasid_allocator_lock needed to be a spinlock?

> + 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);

%px shows raw pointers, but I would drop this altogether or use %p.

> + 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

Describe valid values for @cmd and @flags? I guess this function
shouldn't accept IOASID_ALLOC, IOASID_FREE etc

> + */
> +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);
> + }

else ret = -EINVAL?
What about allowing both flags?

> + spin_unlock(&ioasid_allocator_lock);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_notify);
> +
> MODULE_AUTHOR("Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>");
> MODULE_AUTHOR("Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>");
> 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
> * @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,
> +};

May be nicer to prefix these with IOASID_NOTIFY_

> +
> +#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,
> +};

Not used by this patch, can be added later

> +
> +/**
> + * 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);

These need stubs for !CONFIG_IOASID

> +
> #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)

Missing set argument

Thanks,
Jean

> +{
> + 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;
> --
> 2.7.4
>

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