iommu/tegra-smmu: Prune IOMMU group when it is released

In order to share groups between multiple devices we keep track of them
in a per-SMMU list. When an IOMMU group is released, a dangling pointer
to it stays around in that list. Fix this by implementing an IOMMU data
release callback for groups where the dangling pointer can be removed.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20200806155404.3936074-4-thierry.reding@gmail.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/tegra-smmu.c

@@ -19,6 +19,7 @@
 
 struct tegra_smmu_group {
 	struct list_head list;
+	struct tegra_smmu *smmu;
 	const struct tegra_smmu_group_soc *soc;
 	struct iommu_group *group;
 };
@@ -813,6 +814,16 @@ tegra_smmu_find_group(struct tegra_smmu *smmu, unsigned int swgroup)
 	return NULL;
 }
 
+static void tegra_smmu_group_release(void *iommu_data)
+{
+	struct tegra_smmu_group *group = iommu_data;
+	struct tegra_smmu *smmu = group->smmu;
+
+	mutex_lock(&smmu->lock);
+	list_del(&group->list);
+	mutex_unlock(&smmu->lock);
+}
+
 static struct iommu_group *tegra_smmu_group_get(struct tegra_smmu *smmu,
 						unsigned int swgroup)
 {
@@ -840,6 +851,7 @@ static struct iommu_group *tegra_smmu_group_get(struct tegra_smmu *smmu,
 	}
 
 	INIT_LIST_HEAD(&group->list);
+	group->smmu = smmu;
 	group->soc = soc;
 
 	group->group = iommu_group_alloc();
@@ -849,6 +861,7 @@ static struct iommu_group *tegra_smmu_group_get(struct tegra_smmu *smmu,
 		return NULL;
 	}
 
+	iommu_group_set_iommudata(group->group, group, tegra_smmu_group_release);
 	iommu_group_set_name(group->group, soc->name);
 	list_add_tail(&group->list, &smmu->groups);
 	mutex_unlock(&smmu->lock);