diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 6ba2c1dd1d87..a5431ce3007b 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -664,12 +664,21 @@ static inline char *ublk_queue_cmd_buf(struct ublk_device *ub, int q_id)
 	return ublk_get_queue(ub, q_id)->io_cmd_buf;
 }
 
+static inline int __ublk_queue_cmd_buf_size(int depth)
+{
+	return round_up(depth * sizeof(struct ublksrv_io_desc), PAGE_SIZE);
+}
+
 static inline int ublk_queue_cmd_buf_size(struct ublk_device *ub, int q_id)
 {
 	struct ublk_queue *ubq = ublk_get_queue(ub, q_id);
 
-	return round_up(ubq->q_depth * sizeof(struct ublksrv_io_desc),
-			PAGE_SIZE);
+	return __ublk_queue_cmd_buf_size(ubq->q_depth);
+}
+
+static int ublk_max_cmd_buf_size(void)
+{
+	return __ublk_queue_cmd_buf_size(UBLK_MAX_QUEUE_DEPTH);
 }
 
 static inline bool ublk_queue_can_use_recovery_reissue(
@@ -1322,7 +1331,7 @@ static int ublk_ch_mmap(struct file *filp, struct vm_area_struct *vma)
 {
 	struct ublk_device *ub = filp->private_data;
 	size_t sz = vma->vm_end - vma->vm_start;
-	unsigned max_sz = UBLK_MAX_QUEUE_DEPTH * sizeof(struct ublksrv_io_desc);
+	unsigned max_sz = ublk_max_cmd_buf_size();
 	unsigned long pfn, end, phys_off = vma->vm_pgoff << PAGE_SHIFT;
 	int q_id, ret = 0;