From bebee6d8f540f6996d9ac5022b992b61cf01028d Mon Sep 17 00:00:00 2001
From: Matthew Leach <dev@mattleach.net>
Date: Wed, 17 Dec 2025 22:09:46 +0000
Subject: [PATCH] libkernel: address: ensure `to_pfn` can only be called on PA

calculating a PFN from a VA makes no sense since it could be mapped to
any address. Therefore, ensure that it can *only* be called on PAs.
---
 libkernel/src/memory/address.rs |  8 ++++----
 libkernel/src/memory/page.rs    |  6 ++++--
 libkernel/src/memory/region.rs  | 20 ++++++++++----------
 3 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/libkernel/src/memory/address.rs b/libkernel/src/memory/address.rs
index 828ecf1..449ae3e 100644
--- a/libkernel/src/memory/address.rs
+++ b/libkernel/src/memory/address.rs
@@ -164,10 +164,6 @@ impl<K: MemKind, T> Address<K, T> {
     pub fn is_null(self) -> bool {
         self.inner == 0
     }
-
-    pub fn to_pfn(&self) -> PageFrame {
-        PageFrame::from_pfn(self.inner >> PAGE_SHIFT)
-    }
 }
 
 impl<K: MemKind, T: Sized> Address<K, T> {
@@ -294,6 +290,10 @@ impl PA {
     pub fn cast<T>(self) -> TPA<T> {
         TPA::from_value(self.value())
     }
+
+    pub fn to_pfn(&self) -> PageFrame {
+        PageFrame::from_pfn(self.inner >> PAGE_SHIFT)
+    }
 }
 
 /// Trait for translating between physical and virtual addresses.
diff --git a/libkernel/src/memory/page.rs b/libkernel/src/memory/page.rs
index 9e2298f..c320689 100644
--- a/libkernel/src/memory/page.rs
+++ b/libkernel/src/memory/page.rs
@@ -79,8 +79,10 @@ impl<A: CpuOps, G: PageAllocGetter<A>, T: AddressTranslator<()>> ClaimedPage<A,
 
     /// Takes ownership of the page at pfn.
     ///
-    /// SAFETY: Ensure that the calling context does indeed own this page.
-    /// Otherwise, the page may be free'd when it's owned by another context.
+    /// # Safety
+    /// 
+    /// Ensure that the calling context does indeed own this page. Otherwise,
+    /// the page may be free'd when it's owned by another context.
     pub unsafe fn from_pfn(pfn: PageFrame) -> Self {
         Self(
             unsafe {
diff --git a/libkernel/src/memory/region.rs b/libkernel/src/memory/region.rs
index cc009c2..8b83760 100644
--- a/libkernel/src/memory/region.rs
+++ b/libkernel/src/memory/region.rs
@@ -372,6 +372,16 @@ impl<T: MemKind> MemoryRegion<T> {
             }
         })
     }
+}
+
+/// A memory region in physical address space.
+pub type PhysMemoryRegion = MemoryRegion<Physical>;
+
+impl PhysMemoryRegion {
+    /// Map the physical region to virtual space using a translator.
+    pub fn map_via<T: AddressTranslator<()>>(self) -> VirtMemoryRegion {
+        VirtMemoryRegion::new(self.address.to_va::<T>(), self.size)
+    }
 
     pub fn iter_pfns(self) -> impl Iterator<Item = PageFrame> {
         let mut count = 0;
@@ -391,16 +401,6 @@ impl<T: MemKind> MemoryRegion<T> {
     }
 }
 
-/// A memory region in physical address space.
-pub type PhysMemoryRegion = MemoryRegion<Physical>;
-
-impl PhysMemoryRegion {
-    /// Map the physical region to virtual space using a translator.
-    pub fn map_via<T: AddressTranslator<()>>(self) -> VirtMemoryRegion {
-        VirtMemoryRegion::new(self.address.to_va::<T>(), self.size)
-    }
-}
-
 /// A memory region in virtual address space.
 pub type VirtMemoryRegion = MemoryRegion<Virtual>;