From 0d2d41dcdac5a269c2f473d238fcc93c5026f242 Mon Sep 17 00:00:00 2001
From: Aiken Harris <harraiken91@gmail.com>
Date: Mon, 29 Dec 2025 14:52:04 +0100
Subject: [PATCH] Introduce page fault handling infrastructure

---
 xtoskrnl/CMakeLists.txt        |  1 +
 xtoskrnl/includes/mm.hh        |  1 +
 xtoskrnl/includes/mm/pfault.hh | 25 +++++++++++++++++++++++
 xtoskrnl/mm/amd64/pfault.cc    | 26 ++++++++++++++++++++++++
 xtoskrnl/mm/i686/pfault.cc     | 36 ++++++++++++++++++++++++++++++++++
 5 files changed, 89 insertions(+)
 create mode 100644 xtoskrnl/includes/mm/pfault.hh
 create mode 100644 xtoskrnl/mm/amd64/pfault.cc
 create mode 100644 xtoskrnl/mm/i686/pfault.cc

diff --git a/xtoskrnl/CMakeLists.txt b/xtoskrnl/CMakeLists.txt
index e879b97..bd31b8e 100644
--- a/xtoskrnl/CMakeLists.txt
+++ b/xtoskrnl/CMakeLists.txt
@@ -54,6 +54,7 @@ list(APPEND XTOSKRNL_SOURCE
     ${XTOSKRNL_SOURCE_DIR}/mm/${ARCH}/mmgr.cc
     ${XTOSKRNL_SOURCE_DIR}/mm/${ARCH}/pagemap.cc
     ${XTOSKRNL_SOURCE_DIR}/mm/${ARCH}/paging.cc
+    ${XTOSKRNL_SOURCE_DIR}/mm/${ARCH}/pfault.cc
     ${XTOSKRNL_SOURCE_DIR}/mm/${ARCH}/pfn.cc
     ${XTOSKRNL_SOURCE_DIR}/mm/${ARCH}/pte.cc
     ${XTOSKRNL_SOURCE_DIR}/mm/colors.cc
diff --git a/xtoskrnl/includes/mm.hh b/xtoskrnl/includes/mm.hh
index b34863d..5c2e568 100644
--- a/xtoskrnl/includes/mm.hh
+++ b/xtoskrnl/includes/mm.hh
@@ -19,6 +19,7 @@
 #include <mm/hlpool.hh>
 #include <mm/kpool.hh>
 #include <mm/mmgr.hh>
+#include <mm/pfault.hh>
 #include <mm/pfn.hh>
 
 #endif /* __XTOSKRNL_MM_HH */
diff --git a/xtoskrnl/includes/mm/pfault.hh b/xtoskrnl/includes/mm/pfault.hh
new file mode 100644
index 0000000..30e2e49
--- /dev/null
+++ b/xtoskrnl/includes/mm/pfault.hh
@@ -0,0 +1,25 @@
+/**
+ * PROJECT:         ExectOS
+ * COPYRIGHT:       See COPYING.md in the top level directory
+ * FILE:            xtoskrnl/includes/mm/pfault.hh
+ * DESCRIPTION:     Page fault support
+ * DEVELOPERS:      Aiken Harris <harraiken91@gmail.com>
+ */
+
+#ifndef __XTOSKRNL_MM_PFAULT_HH
+#define __XTOSKRNL_MM_PFAULT_HH
+
+#include <xtos.hh>
+
+
+/* Memory Manager */
+namespace MM
+{
+    class PageFault
+    {
+        public:
+            STATIC XTFASTCALL XTSTATUS CheckPdeForPagedPool(IN PVOID VirtualAddress);
+    };
+}
+
+#endif /* __XTOSKRNL_MM_PFAULT_HH */
diff --git a/xtoskrnl/mm/amd64/pfault.cc b/xtoskrnl/mm/amd64/pfault.cc
new file mode 100644
index 0000000..a3d5b9d
--- /dev/null
+++ b/xtoskrnl/mm/amd64/pfault.cc
@@ -0,0 +1,26 @@
+/**
+ * PROJECT:         ExectOS
+ * COPYRIGHT:       See COPYING.md in the top level directory
+ * FILE:            xtoskrnl/mm/amd64/pfault.cc
+ * DESCRIPTION:     Page fault support for AMD64 architecture
+ * DEVELOPERS:      Aiken Harris <harraiken91@gmail.com>
+ */
+
+#include <xtos.hh>
+
+
+/**
+ * Evaluates the PDE for for paged pool and per-session mappings.
+ *
+ * @param VirtualAddress
+ *        Specifies the virtual address to verify.
+ *
+ * @return This routine returns ACCESS_VIOLATION regardless PML4 or PML5 is used.
+ */
+XTFASTCALL
+XTSTATUS
+MM::PageFault::CheckPdeForPagedPool(IN PVOID VirtualAddress)
+{
+    /* Return access violation */
+    return STATUS_ACCESS_VIOLATION;
+}
diff --git a/xtoskrnl/mm/i686/pfault.cc b/xtoskrnl/mm/i686/pfault.cc
new file mode 100644
index 0000000..3b6a8e6
--- /dev/null
+++ b/xtoskrnl/mm/i686/pfault.cc
@@ -0,0 +1,36 @@
+/**
+ * PROJECT:         ExectOS
+ * COPYRIGHT:       See COPYING.md in the top level directory
+ * FILE:            xtoskrnl/mm/i686/pfault.cc
+ * DESCRIPTION:     Page fault support for i686 architecture
+ * DEVELOPERS:      Aiken Harris <harraiken91@gmail.com>
+ */
+
+#include <xtos.hh>
+
+
+/**
+ * Evaluates the PDE for for paged pool and per-session mappings.
+ *
+ * @param VirtualAddress
+ *        Specifies the virtual address to verify.
+ *
+ * @return This routine returns ACCESS_VIOLATION on PML3 or status code on PML2.
+ */
+XTFASTCALL
+XTSTATUS
+MM::PageFault::CheckPdeForPagedPool(IN PVOID VirtualAddress)
+{
+    /* Check if XPA is enabled */
+    if(MM::Paging::GetXpaStatus())
+    {
+        /* Access violation for PML3 */
+        return STATUS_ACCESS_VIOLATION;
+    }
+
+    /* Unimplemented path for PML2 */
+    UNIMPLEMENTED;
+
+    /* Temporarily, just return access violation */
+    return STATUS_ACCESS_VIOLATION;
+}