diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
index b9d690327eae1..9b3ded518f83f 100644
--- a/drivers/iommu/mtk_iommu.c
+++ b/drivers/iommu/mtk_iommu.c
@@ -469,15 +469,16 @@ static int mtk_iommu_attach_device(struct iommu_domain *domain,
 		dom->data = data;
 	}
 
+	mutex_lock(&data->mutex);
 	if (!data->m4u_dom) { /* Initialize the M4U HW */
 		ret = pm_runtime_resume_and_get(m4udev);
 		if (ret < 0)
-			return ret;
+			goto err_unlock;
 
 		ret = mtk_iommu_hw_init(data);
 		if (ret) {
 			pm_runtime_put(m4udev);
-			return ret;
+			goto err_unlock;
 		}
 		data->m4u_dom = dom;
 		writel(dom->cfg.arm_v7s_cfg.ttbr & MMU_PT_ADDR_MASK,
@@ -485,9 +486,14 @@ static int mtk_iommu_attach_device(struct iommu_domain *domain,
 
 		pm_runtime_put(m4udev);
 	}
+	mutex_unlock(&data->mutex);
 
 	mtk_iommu_config(data, dev, true, domid);
 	return 0;
+
+err_unlock:
+	mutex_unlock(&data->mutex);
+	return ret;
 }
 
 static void mtk_iommu_detach_device(struct iommu_domain *domain,
@@ -627,6 +633,7 @@ static struct iommu_group *mtk_iommu_device_group(struct device *dev)
 	if (domid < 0)
 		return ERR_PTR(domid);
 
+	mutex_lock(&data->mutex);
 	group = data->m4u_group[domid];
 	if (!group) {
 		group = iommu_group_alloc();
@@ -635,6 +642,7 @@ static struct iommu_group *mtk_iommu_device_group(struct device *dev)
 	} else {
 		iommu_group_ref_get(group);
 	}
+	mutex_unlock(&data->mutex);
 	return group;
 }
 
@@ -909,6 +917,7 @@ static int mtk_iommu_probe(struct platform_device *pdev)
 	}
 
 	platform_set_drvdata(pdev, data);
+	mutex_init(&data->mutex);
 
 	ret = iommu_device_sysfs_add(&data->iommu, dev, NULL,
 				     "mtk-iommu.%pa", &ioaddr);
diff --git a/drivers/iommu/mtk_iommu.h b/drivers/iommu/mtk_iommu.h
index f81fa8862ed04..f413546ac6e57 100644
--- a/drivers/iommu/mtk_iommu.h
+++ b/drivers/iommu/mtk_iommu.h
@@ -80,6 +80,8 @@ struct mtk_iommu_data {
 
 	struct dma_iommu_mapping	*mapping; /* For mtk_iommu_v1.c */
 
+	struct mutex			mutex; /* Protect m4u_group/m4u_dom above */
+
 	struct list_head		list;
 	struct mtk_smi_larb_iommu	larb_imu[MTK_LARB_NR_MAX];
 };