On 2020-06-27 04:15, Lu Baolu wrote:
The hardware assistant vfio mediated device is a use case of iommu
aux-domain. The interactions between vfio/mdev and iommu during mdev
creation and passthr are:

- Create a group for mdev with iommu_group_alloc();
- Add the device to the group with
         group = iommu_group_alloc();
         if (IS_ERR(group))
                 return PTR_ERR(group);

         ret = iommu_group_add_device(group, &mdev->dev);
         if (!ret)
                 dev_info(&mdev->dev, "MDEV: group_id = %d\n",
- Allocate an aux-domain
- Attach the aux-domain to the physical device from which the mdev is

In the whole process, an iommu group was allocated for the mdev and an
iommu domain was attached to the group, but the group->domain leaves
NULL. As the result, iommu_get_domain_for_dev() doesn't work anymore.

This adds iommu_group_get/set_domain() so that group->domain could be
managed whenever a domain is attached or detached through the aux-domain

Letting external callers poke around directly in the internals of iommu_group doesn't look right to me.

If a regular device is attached to one or more aux domains for PASID use, iommu_get_domain_for_dev() is still going to return the primary domain, so why should it be expected to behave differently for mediated devices? AFAICS it's perfectly legitimate to have no primary domain if traffic-without-PASID is invalid.


Fixes: 7bd50f0cd2fd5 ("vfio/type1: Add domain at(de)taching group helpers")
Signed-off-by: Lu Baolu <baolu...@linux.intel.com>
  drivers/iommu/iommu.c | 28 ++++++++++++++++++++++++++++
  include/linux/iommu.h | 14 ++++++++++++++
  2 files changed, 42 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index d43120eb1dc5..e2b665303d70 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -715,6 +715,34 @@ int iommu_group_set_name(struct iommu_group *group, const 
char *name)
+ * iommu_group_get_domain - get domain of a group
+ * @group: the group
+ *
+ * This is called to get the domain of a group.
+ */
+struct iommu_domain *iommu_group_get_domain(struct iommu_group *group)
+       return group->domain;
+ * iommu_group_set_domain - set domain for a group
+ * @group: the group
+ * @domain: iommu domain
+ *
+ * This is called to set the domain for a group. In aux-domain case, a domain
+ * might attach or detach to an iommu group through the aux-domain apis, but
+ * the group->domain doesn't get a chance to be updated there.
+ */
+void iommu_group_set_domain(struct iommu_group *group,
+                           struct iommu_domain *domain)
+       group->domain = domain;
  static int iommu_create_device_direct_mappings(struct iommu_group *group,
                                               struct device *dev)
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 5f0b7859d2eb..ff88d548a870 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -496,6 +496,9 @@ extern void iommu_group_set_iommudata(struct iommu_group 
                                      void *iommu_data,
                                      void (*release)(void *iommu_data));
  extern int iommu_group_set_name(struct iommu_group *group, const char *name);
+extern struct iommu_domain *iommu_group_get_domain(struct iommu_group *group);
+extern void iommu_group_set_domain(struct iommu_group *group,
+                                  struct iommu_domain *domain);
  extern int iommu_group_add_device(struct iommu_group *group,
                                  struct device *dev);
  extern void iommu_group_remove_device(struct device *dev);
@@ -840,6 +843,17 @@ static inline int iommu_group_set_name(struct iommu_group 
        return -ENODEV;
+static inline
+struct iommu_domain *iommu_group_get_domain(struct iommu_group *group)
+       return NULL;
+static inline void iommu_group_set_domain(struct iommu_group *group,
+                                         struct iommu_domain *domain)
  static inline int iommu_group_add_device(struct iommu_group *group,
                                         struct device *dev)

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