diff --git a/drivers/ub/obmm/obmm_core.h b/drivers/ub/obmm/obmm_core.h
index 4d844334dbadb5f77eb7b03cab065adb22771d26..ff3e717754efc1b0cd783b1534e09c7275076875 100644
--- a/drivers/ub/obmm/obmm_core.h
+++ b/drivers/ub/obmm/obmm_core.h
@@ -87,6 +87,7 @@ struct obmm_region {
 
 	struct cdev cdevice;
 	struct device device;
+	atomic_t device_released;
 
 	refcount_t refcnt;
 
diff --git a/drivers/ub/obmm/obmm_export.c b/drivers/ub/obmm/obmm_export.c
index e1ec90cf15dd476f8471e3358dab16411930aeb8..237eb1e122f92a173fff41c1f9581a2431f8088f 100644
--- a/drivers/ub/obmm/obmm_export.c
+++ b/drivers/ub/obmm/obmm_export.c
@@ -25,6 +25,7 @@
 #include "obmm_core.h"
 #include "obmm_cache.h"
 #include "obmm_export.h"
+#include "obmm_shm_dev.h"
 
 int export_flags_to_region_flags(unsigned long *region_flags, unsigned long user_flags)
 {
@@ -266,6 +267,7 @@ int set_export_vendor(struct obmm_export_region *e_reg, const void __user *vendo
 
 void free_export_region(struct obmm_export_region *e_reg)
 {
+	wait_until_dev_released(&e_reg->region);
 	if (e_reg->vendor_len)
 		kfree(e_reg->vendor_info);
 
diff --git a/drivers/ub/obmm/obmm_export_from_pool.c b/drivers/ub/obmm/obmm_export_from_pool.c
index dabf5373ea2cd05b78dd0a228da24326b99e4b21..daa4214955da9e615638a48f97829fba4d3dbf8c 100644
--- a/drivers/ub/obmm/obmm_export_from_pool.c
+++ b/drivers/ub/obmm/obmm_export_from_pool.c
@@ -255,6 +255,8 @@ static struct obmm_export_region *alloc_region_from_cmd(struct obmm_cmd_export *
 	if (e_reg == NULL)
 		return ERR_PTR(-ENOMEM);
 
+	atomic_set(&e_reg->region.device_released, 1);
+
 	e_reg->region.type = OBMM_EXPORT_REGION;
 	e_reg->region.mem_size = total_size;
 	e_reg->region.mem_cap = OBMM_MEM_ALLOW_CACHEABLE_MMAP | OBMM_MEM_ALLOW_NONCACHEABLE_MMAP;
diff --git a/drivers/ub/obmm/obmm_export_from_user.c b/drivers/ub/obmm/obmm_export_from_user.c
index bd0663bb197f492b83b6811472c6ad851339bbee..f136d3398753a3eb97e36a003c18f592b65e53d0 100644
--- a/drivers/ub/obmm/obmm_export_from_user.c
+++ b/drivers/ub/obmm/obmm_export_from_user.c
@@ -255,6 +255,10 @@ static int obmm_cmd_export_pid_allowed(struct obmm_cmd_export_pid *cmd)
 		pr_err("ALLOW_MMAP flag is not allowed in export_user_addr.\n");
 		return -EINVAL;
 	}
+	if (cmd->flags & OBMM_EXPORT_FLAG_FAST) {
+		pr_err("FAST flag is not allowed in export_user_addr.\n");
+		return -EINVAL;
+	}
 
 	if (cmd->length == 0) {
 		pr_err("export sizeof 0 memory is not allowed.\n");
@@ -279,6 +283,8 @@ alloc_export_region_from_obmm_cmd_export_pid(const struct obmm_cmd_export_pid *e
 	if (e_reg == NULL)
 		return ERR_PTR(-ENOMEM);
 
+	atomic_set(&e_reg->region.device_released, 1);
+
 	e_reg->mem_desc_pid.pid = export_pid->pid;
 	e_reg->mem_desc_pid.user_va = export_pid->va;
 	e_reg->region.mem_size = export_pid->length;
diff --git a/drivers/ub/obmm/obmm_import.c b/drivers/ub/obmm/obmm_import.c
index 18f59efa90c6014a1b4c6b0f219b8718a14c61d9..4a56a86f68f273ff343d0a2d409982668f18393c 100644
--- a/drivers/ub/obmm/obmm_import.c
+++ b/drivers/ub/obmm/obmm_import.c
@@ -16,6 +16,7 @@
 #include "obmm_preimport.h"
 #include "obmm_resource.h"
 #include "obmm_addr_check.h"
+#include "obmm_shm_dev.h"
 
 static void set_import_region_datapath(const struct obmm_import_region *i_reg,
 				       struct obmm_datapath *datapath)
@@ -415,6 +416,8 @@ int obmm_import(struct obmm_cmd_import *cmd_import)
 	if (i_reg == NULL)
 		return -ENOMEM;
 
+	atomic_set(&i_reg->region.device_released, 1);
+
 	/* arguments to region (logs produced by callee) */
 	retval = init_import_region_from_cmd(cmd_import, i_reg);
 	if (retval)
@@ -455,6 +458,7 @@ int obmm_import(struct obmm_cmd_import *cmd_import)
 out_region_uninit:
 	uninit_obmm_region(&i_reg->region);
 out_free_ireg:
+	wait_until_dev_released(&i_reg->region);
 	kfree(i_reg);
 	return retval;
 }
@@ -493,6 +497,7 @@ int obmm_unimport(const struct obmm_cmd_unimport *cmd_unimport)
 
 	deregister_obmm_region(reg);
 	uninit_obmm_region(reg);
+	wait_until_dev_released(&i_reg->region);
 	kfree(i_reg);
 
 	pr_info("%s: mem_id=%llu completed.\n", __func__, cmd_unimport->mem_id);
diff --git a/drivers/ub/obmm/obmm_shm_dev.c b/drivers/ub/obmm/obmm_shm_dev.c
index 0272287fea640ca23b16ee1302b03240513b3ffb..0814c37d12b46ca600fb95f5a96868548003d44d 100644
--- a/drivers/ub/obmm/obmm_shm_dev.c
+++ b/drivers/ub/obmm/obmm_shm_dev.c
@@ -310,7 +310,7 @@ static int obmm_shm_fops_mmap(struct file *file, struct vm_area_struct *vma)
 	unsigned long size, offset;
 	uint8_t mem_state;
 	enum obmm_mmap_mode old_mmap_mode;
-	enum obmm_mmap_granu mmap_granu;
+	enum obmm_mmap_granu mmap_granu, init_mmap_granu;
 	int ret;
 	bool cacheable, o_sync;
 
@@ -331,21 +331,23 @@ static int obmm_shm_fops_mmap(struct file *file, struct vm_area_struct *vma)
 
 	if (offset & OBMM_MMAP_FLAG_HUGETLB_PMD) {
 		pr_debug("trying hugepage mmap\n");
-		mmap_granu = OBMM_MMAP_GRANU_PMD;
 		offset &= ~OBMM_MMAP_FLAG_HUGETLB_PMD;
 		if (vma->vm_start % PMD_SIZE || vma->vm_end % PMD_SIZE) {
 			pr_err("error running huge mmap for not pmd-aligned vma: %#lx-%#lx\n",
 				vma->vm_start, vma->vm_end);
 			return -EINVAL;
 		}
+		mmap_granu = OBMM_MMAP_GRANU_PMD;
 	} else {
 		mmap_granu = OBMM_MMAP_GRANU_PAGE;
 	}
+	init_mmap_granu = reg->mmap_granu;
 	if (reg->mmap_granu == OBMM_MMAP_GRANU_NONE) {
 		reg->mmap_granu = mmap_granu;
 	} else if (reg->mmap_granu != mmap_granu) {
 		pr_err("map with PAGE_SIZE and PMD_SIZE granu should not be mixed on the same region\n");
-		return -EINVAL;
+		ret = -EPERM;
+		goto err_reset_mmap_granu;
 	}
 
 	vma->vm_pgoff = offset >> PAGE_SHIFT;
@@ -353,7 +355,8 @@ static int obmm_shm_fops_mmap(struct file *file, struct vm_area_struct *vma)
 	if (offset >= reg->mem_size || size > reg->mem_size - offset) {
 		pr_err("mmap region %d: offset:%#lx, size:%#lx over region size: %#llx",
 		       reg->regionid, offset, size, reg->mem_size);
-		return -EINVAL;
+		ret = -EINVAL;
+		goto err_reset_mmap_granu;
 	}
 
 	/*
@@ -404,6 +407,11 @@ static int obmm_shm_fops_mmap(struct file *file, struct vm_area_struct *vma)
 			ret = init_ownership_info(reg);
 			if (ret)
 				goto err_release_local_state_info;
+			/*
+			 * after ownership_info initialized, mmap_granu should not be
+			 * reset to OBMM_MMAP_GRANU_NONE.
+			 */
+			init_mmap_granu = reg->mmap_granu;
 			ret = check_mmap_allowed(reg, vma, mem_state);
 			if (ret)
 				goto err_release_local_state_info;
@@ -454,6 +462,8 @@ static int obmm_shm_fops_mmap(struct file *file, struct vm_area_struct *vma)
 		reg->mmap_mode = OBMM_MMAP_INIT;
 err_mutex_unlock:
 	mutex_unlock(&reg->state_mutex);
+err_reset_mmap_granu:
+	reg->mmap_granu = init_mmap_granu;
 	return ret;
 }
 
@@ -881,9 +891,18 @@ const struct file_operations obmm_shm_fops = { .owner = THIS_MODULE,
 
 static void obmm_shm_dev_release(struct device *dev)
 {
+	struct obmm_region *reg = container_of(dev, struct obmm_region, device);
+
+	atomic_set(&reg->device_released, 1);
 	module_put(THIS_MODULE);
 }
 
+void wait_until_dev_released(struct obmm_region *reg)
+{
+	while (atomic_read(&reg->device_released) == 0)
+		cpu_relax();
+}
+
 int obmm_shm_dev_add(struct obmm_region *reg)
 {
 	int ret;
@@ -918,6 +937,8 @@ int obmm_shm_dev_add(struct obmm_region *reg)
 		goto err_put_dev;
 	}
 
+	atomic_set(&reg->device_released, 0);
+
 	return 0;
 
 	/* NOTE: If the device is properly initialized, the refcount of module
diff --git a/drivers/ub/obmm/obmm_shm_dev.h b/drivers/ub/obmm/obmm_shm_dev.h
index bfced747a2aafd83093a7a38f1ec599e54616d5e..e0bf3553a3ce61f30cb3a829a2ad58439c2be21a 100644
--- a/drivers/ub/obmm/obmm_shm_dev.h
+++ b/drivers/ub/obmm/obmm_shm_dev.h
@@ -12,5 +12,7 @@ int obmm_shm_dev_init(void);
 void obmm_shm_dev_exit(void);
 int obmm_shm_dev_add(struct obmm_region *reg);
 void obmm_shm_dev_del(struct obmm_region *reg);
+void wait_until_dev_released(struct obmm_region *reg);
+
 
 #endif