diff --git a/drivers/iommu/iommufd/selftest.c b/drivers/iommu/iommufd/selftest.c
index 654ed3339095..62bfeb7a35d8 100644
--- a/drivers/iommu/iommufd/selftest.c
+++ b/drivers/iommu/iommufd/selftest.c
@@ -1313,7 +1313,7 @@ static int iommufd_test_dirty(struct iommufd_ucmd *ucmd, unsigned int mockpt_id,
 			      unsigned long page_size, void __user *uptr,
 			      u32 flags)
 {
-	unsigned long bitmap_size, i, max;
+	unsigned long i, max;
 	struct iommu_test_cmd *cmd = ucmd->cmd;
 	struct iommufd_hw_pagetable *hwpt;
 	struct mock_iommu_domain *mock;
@@ -1334,15 +1334,14 @@ static int iommufd_test_dirty(struct iommufd_ucmd *ucmd, unsigned int mockpt_id,
 	}
 
 	max = length / page_size;
-	bitmap_size = DIV_ROUND_UP(max, BITS_PER_BYTE);
-
-	tmp = kvzalloc(bitmap_size, GFP_KERNEL_ACCOUNT);
+	tmp = kvzalloc(DIV_ROUND_UP(max, BITS_PER_LONG) * sizeof(unsigned long),
+		       GFP_KERNEL_ACCOUNT);
 	if (!tmp) {
 		rc = -ENOMEM;
 		goto out_put;
 	}
 
-	if (copy_from_user(tmp, uptr, bitmap_size)) {
+	if (copy_from_user(tmp, uptr,DIV_ROUND_UP(max, BITS_PER_BYTE))) {
 		rc = -EFAULT;
 		goto out_free;
 	}