Signed-off-by: Kenneth Lee <redacted>
---
 drivers/iommu/iommu.c | 28 +++++++++++++++++++++++++++-
 include/linux/iommu.h |  2 ++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 63b37563db7e..a832aafe660d 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c

@@ -54,6 +54,9 @@ struct iommu_group {
 	int id;
 	struct iommu_domain *default_domain;
 	struct iommu_domain *domain;
+	atomic_t domain_shared_ref; /* Number of user of current domain.
+				     * The domain cannot be modified if ref >

0
+				     */
 };

 struct group_device {

@@ -353,6 +356,7 @@ struct iommu_group *iommu_group_alloc(void)
 		return ERR_PTR(ret);
 	}
 	group->id = ret;
+	atomic_set(&group->domain_shared_ref, 0);

 	ret = kobject_init_and_add(&group->kobj, &iommu_group_ktype,
 				   NULL, "%d", group->id);

@@ -482,6 +486,25 @@ int iommu_group_set_name(struct iommu_group

*group, const char *name)
 }
 EXPORT_SYMBOL_GPL(iommu_group_set_name);

+struct iommu_domain *iommu_group_share_domain(struct
iommu_group *group)
+{
+	/* the domain can be shared only when the default domain is used
*/
+	/* todo: more shareable check */
+	if (group->domain != group->default_domain)
+		return ERR_PTR(-EINVAL);
+
+	atomic_inc(&group->domain_shared_ref);
+	return group->domain;
+}
+EXPORT_SYMBOL_GPL(iommu_group_share_domain);
+
+void iommu_group_unshare_domain(struct iommu_group *group)
+{
+	atomic_dec(&group->domain_shared_ref);
+	WARN_ON(atomic_read(&group->domain_shared_ref) < 0);
+}
+EXPORT_SYMBOL_GPL(iommu_group_unshare_domain);
+
 static int iommu_group_create_direct_mappings(struct iommu_group
*group,
 					      struct device *dev)
 {

@@ -1401,7 +1424,8 @@ static int __iommu_attach_group(struct

iommu_domain *domain,
 {
 	int ret;

-	if (group->default_domain && group->domain != group-

quoted

default_domain)

+	if ((group->default_domain && group->domain != group-

quoted

default_domain) ||

+	     atomic_read(&group->domain_shared_ref) > 0)
 		return -EBUSY;

 	ret = __iommu_group_for_each_dev(group, domain,

@@ -1438,6 +1462,8 @@ static void __iommu_detach_group(struct

iommu_domain *domain,
 {
 	int ret;

+	WARN_ON(atomic_read(&group->domain_shared_ref) > 0);
+
 	if (!group->default_domain) {
 		__iommu_group_for_each_dev(group, domain,
 					   iommu_group_do_detach_device);

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 19938ee6eb31..278d60e3ec39 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h

@@ -349,6 +349,8 @@ extern int iommu_domain_get_attr(struct

iommu_domain *domain, enum iommu_attr,
 				 void *data);
 extern int iommu_domain_set_attr(struct iommu_domain *domain, enum
iommu_attr,
 				 void *data);
+extern struct iommu_domain *iommu_group_share_domain(struct
iommu_group *group);
+extern void iommu_group_unshare_domain(struct iommu_group *group);

 /* Window handling function prototypes */
 extern int iommu_domain_window_enable(struct iommu_domain
*domain, u32 wnd_nr,
--
2.17.1