RE: [PATCH v10 3/6] iommufd: Add iommufd_access_change_ioas(_id) helpers

From: Nicolin Chen nicolinc@nvidia.com Sent: Friday, July 28, 2023 4:25 AM

+static int iommufd_access_change_ioas(struct iommufd_access *access,

• 		      struct iommufd_ioas *new_ioas)
  

+{

• u32 iopt_access_list_id = access->iopt_access_list_id;
• struct iommufd_ioas *cur_ioas = access->ioas;
• int rc;
• lockdep_assert_held(&access->ioas_lock);
• /* We are racing with a concurrent detach, bail */
• if (cur_ioas != access->ioas_unpin)

• return -EBUSY;
  

• if (IS_ERR(new_ioas))

• return PTR_ERR(new_ioas);
  

iommufd_access_change_ioas_id() already checks errors.

void iommufd_access_destroy_object(struct iommufd_object *obj) { struct iommufd_access *access = container_of(obj, struct iommufd_access, obj);

• if (access->ioas) {

• iopt_remove_access(&access->ioas->iopt, access,
  

• 		   access->iopt_access_list_id);
  

• refcount_dec(&access->ioas->obj.users);
  

• access->ioas = NULL;
  

• }

• mutex_lock(&access->ioas_lock);
• if (access->ioas)

• WARN_ON(iommufd_access_change_ioas(access, NULL));
  

• mutex_unlock(&access->ioas_lock); iommufd_ctx_put(access->ictx);

}

this changes the behavior of destroy. Previously it always removes the access w/o detecting race while now it will give up and throw out a warning. While I'm fine with this change from bisec p.o.v. it might be good to split this into a separate patch.

void iommufd_access_detach(struct iommufd_access *access) {

• struct iommufd_ioas *cur_ioas = access->ioas;

• int rc;

  mutex_lock(&access->ioas_lock);

• if (WARN_ON(!access->ioas))

• goto out;
  

• /*

• * Set ioas to NULL to block any further iommufd_access_pin_pages().
  

• * iommufd_access_unpin_pages() can continue using access-
  

...

ioas_unpin.

• */
  

• access->ioas = NULL;
• if (access->ops->unmap) {

• if (WARN_ON(!access->ioas)) { mutex_unlock(&access->ioas_lock);

• access->ops->unmap(access->data, 0, ULONG_MAX);
  

• mutex_lock(&access->ioas_lock);
  

• return;
  

  }

• iopt_remove_access(&cur_ioas->iopt, access,

• 	   access->iopt_access_list_id);
  

• refcount_dec(&cur_ioas->obj.users);

-out:

• access->ioas_unpin = NULL;

• rc = iommufd_access_change_ioas(access, NULL);
• WARN_ON(rc);

'rc' can be removed.

Just "WARN_ON(iommufd_access_change_ioas(access, NULL));"

otherwise looks good to me,

Reviewed-by: Kevin Tian kevin.tian@intel.com