iommufd: Add iommufd_access_change_ioas(_id) helpers

The complication of the mutex and refcount will be amplified after we
introduce the replace support for accesses. So, add a preparatory change
of a constitutive helper iommufd_access_change_ioas() and its wrapper
iommufd_access_change_ioas_id(). They can simply take care of existing
iommufd_access_attach() and iommufd_access_detach(), properly sequencing
the refcount puts so that they are truely at the end of the sequence after
we know the IOAS pointer is not required any more.

Link: https://lore.kernel.org/r/da0c462532193b447329c4eb975a596f47e49b70.1690523699.git.nicolinc@nvidia.com
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
index 7a3e866..e5c4084 100644 (file)
--- a/drivers/iommu/iommufd/device.c
+++ b/drivers/iommu/iommufd/device.c
@@ -684,6 +684,70 @@ void iommufd_device_detach(struct iommufd_device *idev)
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_device_detach, IOMMUFD);
 
+/*
+ * On success, it will refcount_inc() at a valid new_ioas and refcount_dec() at
+ * a valid cur_ioas (access->ioas). A caller passing in a valid new_ioas should
+ * call iommufd_put_object() if it does an iommufd_get_object() for a new_ioas.
+ */
+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 (cur_ioas == new_ioas)
+               return 0;
+
+       /*
+        * 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 (new_ioas) {
+               rc = iopt_add_access(&new_ioas->iopt, access);
+               if (rc) {
+                       access->ioas = cur_ioas;
+                       return rc;
+               }
+               refcount_inc(&new_ioas->obj.users);
+       }
+
+       if (cur_ioas) {
+               if (access->ops->unmap) {
+                       mutex_unlock(&access->ioas_lock);
+                       access->ops->unmap(access->data, 0, ULONG_MAX);
+                       mutex_lock(&access->ioas_lock);
+               }
+               iopt_remove_access(&cur_ioas->iopt, access, iopt_access_list_id);
+               refcount_dec(&cur_ioas->obj.users);
+       }
+
+       access->ioas = new_ioas;
+       access->ioas_unpin = new_ioas;
+
+       return 0;
+}
+
+static int iommufd_access_change_ioas_id(struct iommufd_access *access, u32 id)
+{
+       struct iommufd_ioas *ioas = iommufd_get_ioas(access->ictx, id);
+       int rc;
+
+       if (IS_ERR(ioas))
+               return PTR_ERR(ioas);
+       rc = iommufd_access_change_ioas(access, ioas);
+       iommufd_put_object(&ioas->obj);
+       return rc;
+}
+
 void iommufd_access_destroy_object(struct iommufd_object *obj)
 {
        struct iommufd_access *access =
@@ -761,60 +825,29 @@ EXPORT_SYMBOL_NS_GPL(iommufd_access_destroy, IOMMUFD);
 
 void iommufd_access_detach(struct iommufd_access *access)
 {
-       struct iommufd_ioas *cur_ioas = access->ioas;
-
        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;
+       WARN_ON(iommufd_access_change_ioas(access, NULL));
        mutex_unlock(&access->ioas_lock);
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_access_detach, IOMMUFD);
 
 int iommufd_access_attach(struct iommufd_access *access, u32 ioas_id)
 {
-       struct iommufd_ioas *new_ioas;
-       int rc = 0;
+       int rc;
 
        mutex_lock(&access->ioas_lock);
-       if (WARN_ON(access->ioas || access->ioas_unpin)) {
+       if (WARN_ON(access->ioas)) {
                mutex_unlock(&access->ioas_lock);
                return -EINVAL;
        }
 
-       new_ioas = iommufd_get_ioas(access->ictx, ioas_id);
-       if (IS_ERR(new_ioas)) {
-               mutex_unlock(&access->ioas_lock);
-               return PTR_ERR(new_ioas);
-       }
-
-       rc = iopt_add_access(&new_ioas->iopt, access);
-       if (rc) {
-               mutex_unlock(&access->ioas_lock);
-               iommufd_put_object(&new_ioas->obj);
-               return rc;
-       }
-       iommufd_ref_to_users(&new_ioas->obj);
-
-       access->ioas = new_ioas;
-       access->ioas_unpin = new_ioas;
+       rc = iommufd_access_change_ioas_id(access, ioas_id);
        mutex_unlock(&access->ioas_lock);
-       return 0;
+       return rc;
 }
 EXPORT_SYMBOL_NS_GPL(iommufd_access_attach, IOMMUFD);