From e829590d40b6312d994987dd0fdc13fec625c8b2 Mon Sep 17 00:00:00 2001
From: Matthew Leach <dev@mattleach.net>
Date: Wed, 26 Aug 2026 12:03:19 +0100
Subject: [PATCH] libkernel: add `cast_mem_kind`

Add functions to addresses and regions which allow easy casting from one
address space kind to another, while preserving bits.
---
 libkernel/src/memory/address.rs | 11 +++++++++++
 libkernel/src/memory/region.rs  | 15 +++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/libkernel/src/memory/address.rs b/libkernel/src/memory/address.rs
index ccc488da..b2ed0575 100644
--- a/libkernel/src/memory/address.rs
+++ b/libkernel/src/memory/address.rs
@@ -118,6 +118,17 @@ impl<K: MemKind, T> Address<K, T> {
         }
     }
 
+    /// Cast from one address space kind to the other, without modification of
+    /// the address bits.
+    ///
+    /// # Safety
+    ///
+    /// the caller must ensure that the same address is valid in the other
+    /// address space, e.g. through identity mappings.
+    pub const unsafe fn cast_mem_kind<O: MemKind>(self) -> Address<O, T> {
+        Address::from_value(self.value())
+    }
+
     /// Return the underlying raw address value.
     pub const fn value(self) -> usize {
         self.inner
diff --git a/libkernel/src/memory/region.rs b/libkernel/src/memory/region.rs
index 9ef666ca..7bc95394 100644
--- a/libkernel/src/memory/region.rs
+++ b/libkernel/src/memory/region.rs
@@ -53,6 +53,21 @@ impl<T: MemKind> MemoryRegion<T> {
         Self { address, size }
     }
 
+    /// Cast from one address space kind to the other, without modification of
+    /// the address bits.
+    ///
+    /// # Safety
+    ///
+    /// the caller must ensure that the same address is valid in the other
+    /// address space, e.g. through identity mappings.
+    pub const unsafe fn cast_mem_kind<O: MemKind>(self) -> MemoryRegion<O> {
+        // SAFETY: The caller ensures the safety invariant is true.
+        MemoryRegion {
+            address: unsafe { self.address.cast_mem_kind() },
+            size: self.size,
+        }
+    }
+
     /// Create an empty region with a size of 0 and address 0.
     pub const fn empty() -> Self {
         Self {