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

On Fri, Jul 28, 2023 at 04:23:03AM +0000, Tian, Kevin wrote:

...

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.

I've thought about that: given that iommufd_access_change_ioas is a standalone API, though it's not used anywhere else at the moment, it might be safer to have this check again. Otherwise, we would need a line of comments saying that "caller must make sure that the input new_ioas is not holding an error code" or so?

...

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.

You mean the -EBUSY case? That's a good catch..

While I'm fine with this change from bisec p.o.v. it might be good to split this into a separate patch.

Yea, I can do that.

...

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));"

Will do that in v11.

otherwise looks good to me,

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

Thanks! Nic