Re: [PATCH v3 11/14] iommu/ioasid: Support mm type ioasid_set notifications

Jean-Philippe Brucker
2020-10-23T11:43:59Z

On Mon, Sep 28, 2020 at 02:38:38PM -0700, Jacob Pan wrote:
> As a system-wide resource, IOASID is often shared by multiple kernel
> subsystems that are independent of each other. However, at the
> ioasid_set level, these kernel subsystems must communicate with each
> other for ownership checking, event notifications, etc. For example, on
> Intel Scalable IO Virtualization (SIOV) enabled platforms, KVM and VFIO
> instances under the same process/guest must be aware of a shared IOASID
> set.
> IOASID_SET_TYPE_MM token type was introduced to explicitly mark an
> IOASID set that belongs to a process, thus use the same mm_struct
> pointer as a token. Users of the same process can then identify with
> each other based on this token.
>
> This patch introduces MM token specific event registration APIs. Event
> subscribers such as KVM instances can register IOASID event handler
> without the knowledge of its ioasid_set. Event handlers are registered
> based on its mm_struct pointer as a token. In case when subscribers
> register handler *prior* to the creation of the ioasid_set, the
> handler’s notification block is stored in a pending list within IOASID
> core. Once the ioasid_set of the MM token is created, the notification
> block will be registered by the IOASID core.
>
> 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 | 117 +++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/ioasid.h | 15 +++++++
> 2 files changed, 132 insertions(+)
>
> diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
> index 894b17c06ead..d5faeb559a43 100644
> --- a/drivers/iommu/ioasid.c
> +++ b/drivers/iommu/ioasid.c
> @@ -889,6 +889,29 @@ void ioasid_set_put(struct ioasid_set *set)
> }
> EXPORT_SYMBOL_GPL(ioasid_set_put);
>
> +/*
> + * 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 *set;
> + unsigned long index;
> +
> + spin_lock(&ioasid_allocator_lock);

This could deadlock since ioasid_set_put() takes the nb_lock while holding
the allocator_lock.

> +
> + xa_for_each(&ioasid_sets, index, set) {
> + if (set->type == IOASID_SET_TYPE_MM && set->token == token) {
> + refcount_inc(&set->ref);
> + goto exit_unlock;
> + }
> + }
> + set = NULL;
> +exit_unlock:
> + spin_unlock(&ioasid_allocator_lock);
> + return set;
> +}
> +
> /**
> * ioasid_adjust_set - Adjust the quota of an IOASID set
> * @set: IOASID set to be assigned
> @@ -1121,6 +1144,100 @@ void ioasid_unregister_notifier(struct ioasid_set *set,
> }
> EXPORT_SYMBOL_GPL(ioasid_unregister_notifier);
>
> +/**
> + * ioasid_register_notifier_mm - Register a notifier block on the IOASID set
> + * created by the mm_struct pointer as the token
> + *
> + * @mm: the mm_struct token of the ioasid_set
> + * @nb: notfier block to be registered on the ioasid_set

Maybe add that the priority in @nb needs to be set by the caller using a
ioasid_notifier_priority value

> + *
> + * This a variant of ioasid_register_notifier() where the caller intends to
> + * listen to IOASID events belong the ioasid_set created under the same

that belong to

> + * process. Caller is not aware of the ioasid_set, no need to hold reference
> + * of the ioasid_set.
> + */
> +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 (!set) {
> + /* Add to the rsvd list as inactive */
> + curr->active = false;

curr is invalid here

> + } else {
> + /* REVISIT: Only register empty set for now. Can add an option
> + * in the future to playback existing PASIDs.
> + */

You can drop this comment

> + if (set->nr_ioasids) {
> + pr_warn("IOASID set %d not empty\n", set->id);
> + ret = -EBUSY;
> + goto exit_unlock;
> + }
> + curr = kzalloc(sizeof(*curr), GFP_ATOMIC);

Needs to be in the common path, before this block

> + 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);
> + spin_unlock(&ioasid_nb_lock);
> + if (curr->active) {
> + atomic_notifier_chain_unregister(&curr->set->nh,
> + nb);

I think it's possible for ioasid_set_put_locked() to free the set right
after we release the lock, then this unregister() will be use-after-free.
Best keep holding the lock for this.

> + }
> + kfree(curr);
> + return;
> + }
> + }
> + pr_warn("No ioasid set found for mm token %llx\n", (u64)mm);

Use %p

Overall I think error messages in this series could be demoted to
pr_debug, since they're useful when developing users to this API, but
figuring out whether they can be user-triggered and need care is too much
work.

Thanks,
Jean

> + spin_unlock(&ioasid_nb_lock);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_unregister_notifier_mm);
> +
> 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 1b551c99d568..c6cc855aadb6 100644
> --- a/include/linux/ioasid.h
> +++ b/include/linux/ioasid.h
> @@ -132,6 +132,9 @@ void ioasid_unregister_notifier(struct ioasid_set *set,
> void 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)
> {
> @@ -238,5 +241,17 @@ static inline void ioasid_set_for_each_ioasid(struct ioasid_set *sdata,
> void *data)
> {
> }
> +
> +static inline int ioasid_register_notifier_mm(struct mm_struct *mm,
> + struct notifier_block *nb)
> +{
> + return -ENOTSUPP;
> +}
> +
> +static inline void ioasid_unregister_notifier_mm(struct mm_struct *mm,
> + struct notifier_block *nb)
> +{
> +}
> +
> #endif /* CONFIG_IOASID */
> #endif /* __LINUX_IOASID_H */
> --
> 2.7.4
>