iommu/amd: Fix group refcounting

If acpihid_device_group() finds an existing group for the relevant
devid, it should be taking an additional reference on that group.
Otherwise, the caller of iommu_group_get_for_dev() will inadvertently
remove the reference taken by iommu_group_add_device(), and the group
will be freed prematurely if any device is removed.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 754595ee11b6..019e02707cd5 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -373,6 +373,8 @@ static struct iommu_group *acpihid_device_group(struct device *dev)
 
         if (!entry->group)
                 entry->group = generic_device_group(dev);
+        else
+                iommu_group_ref_get(entry->group);
 
         return entry->group;
 }