diff --git a/hbvm/src/vm/mem/mod.rs b/hbvm/src/vm/mem/mod.rs
index 26dc8a3..05bb511 100644
--- a/hbvm/src/vm/mem/mod.rs
+++ b/hbvm/src/vm/mem/mod.rs
@@ -206,9 +206,9 @@ impl Iterator for PageSplitter {
                                 ptr as *mut u8,
                                 perm,
                                 match lvl {
-                                    0 => 4096,
-                                    1 => 1024_usize.pow(2) * 2,
-                                    2 => 1024_usize.pow(3),
+                                    0 => PageSize::Size4K,
+                                    1 => PageSize::Size2M,
+                                    2 => PageSize::Size1G,
                                     _ => return None,
                                 },
                                 self.addr as usize & ((1 << (lvl * 9 + 12)) - 1),
@@ -220,9 +220,9 @@ impl Iterator for PageSplitter {
             return None;
         };
 
-        let avail = (size - offset).clamp(0, self.size);
+        let avail = (size as usize - offset).clamp(0, self.size);
         self.addr += size as u64;
-        self.size = self.size.saturating_sub(size);
+        self.size = self.size.saturating_sub(size as _);
         Some(PageSplitResult {
             ptr: unsafe { base.add(offset) },
             size: avail,
@@ -230,3 +230,10 @@ impl Iterator for PageSplitter {
         })
     }
 }
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum PageSize {
+    Size4K = 4096,
+    Size2M = 1024 * 1024 * 2,
+    Size1G = 1024 * 1024 * 1024,
+}