From 181b0fdf61a805a6833d7b57c8c20f674275270e Mon Sep 17 00:00:00 2001
From: "Chloe M." <chloe@mensia.org>
Date: Tue, 14 Jul 2026 21:25:51 +0000
Subject: [PATCH] ptos/amd64+hal: Add virtual address space forking

Signed-off-by: Chloe M. <chloe@mensia.org>
---
 service/ptos/arch/amd64/cpu/mmu.c | 34 +++++++++++++++++++++++++++++++
 service/ptos/head/hal/mmu.h       |  9 ++++++++
 service/ptos/mm/vm.c              | 13 +++++++++++-
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/service/ptos/arch/amd64/cpu/mmu.c b/service/ptos/arch/amd64/cpu/mmu.c
index c79f7ce..7428b0b 100644
--- a/service/ptos/arch/amd64/cpu/mmu.c
+++ b/service/ptos/arch/amd64/cpu/mmu.c
@@ -260,3 +260,37 @@ HalMmuUnmapPage(MMU_VAS *Vas, UPTR VirtualBase, MMU_PAGESIZE PageSize)
     MdTlbFlushSingle(VirtualBase);
     return STATUS_SUCCESS;
 }
+
+PT_STATUS
+HalMmuForkVas(const MMU_VAS *Source, MMU_VAS *Result)
+{
+    const UPTR *Src;
+    UPTR *Dest;
+    UPTR DestPhysBase;
+    MM_PFN DestPfn;
+
+    if (Source == NULL || Result == NULL) {
+        return STATUS_INVALID_PARAM;
+    }
+
+    DestPfn = MmRequestFrame();
+    if (DestPfn == PFN_ERROR) {
+        return STATUS_NO_MEMORY;
+    }
+
+    DestPhysBase = PFN_TO_ADDRESS(DestPfn);
+    Src = PMA_TO_VMA((Source->Cr3 & PTE_ADDR_MASK));
+    Dest = PMA_TO_VMA(DestPhysBase);
+
+    /* Begin copy */
+    for (USIZE Idx = 0; Idx < 512; ++Idx) {
+        if (Idx < 256) {
+            Dest[Idx] = 0;
+        } else {
+            Dest[Idx] = Src[Idx];
+        }
+    }
+
+    Result->Cr3 = DestPhysBase;
+    return STATUS_SUCCESS;
+}
diff --git a/service/ptos/head/hal/mmu.h b/service/ptos/head/hal/mmu.h
index 7879dfc..e928b2b 100644
--- a/service/ptos/head/hal/mmu.h
+++ b/service/ptos/head/hal/mmu.h
@@ -38,6 +38,15 @@ VOID HalMmuReadVas(MMU_VAS *Result);
  */
 VOID HalMmuWriteVas(const MMU_VAS *Vas);
 
+/*
+ * Fork a virtual address space with the user-portion zeroed
+ * out.
+ *
+ * @Source:  Source VAS to fork from
+ * @Result:  Result is written here
+ */
+PT_STATUS HalMmuForkVas(const MMU_VAS *Source, MMU_VAS *Result);
+
 /*
  * Map a single page of memory
  *
diff --git a/service/ptos/mm/vm.c b/service/ptos/mm/vm.c
index 2c3132e..450d5a2 100644
--- a/service/ptos/mm/vm.c
+++ b/service/ptos/mm/vm.c
@@ -35,6 +35,9 @@ static USIZE PageSizeTable[] = {
     [PAGESIZE_4K] = 0x1000
 };
 
+/* Kernel VAS */
+static MMU_VAS KVas;
+
 /* Bump pointer and vad tree */
 static UPTR VallocBump = VALLOC_BASE;
 static MM_VAD_TREE VadTree;
@@ -138,7 +141,15 @@ MmVmInit(VOID)
 
     HalMmuReadVas(&VasCurrent);
     MmVadTreeInit(&VadTree);
+    Status = HalMmuForkVas(&VasCurrent, &KVas);
+    if (PT_ERROR(Status)) {
+        KeBugCheck(
+            BUGCHECK_OOM,
+            "failed to allocate kernel vas\n"
+        );
+    }
 
+    HalMmuWriteVas(&KVas);
     VirtualStart = VallocBump;
     VallocBump += INITIAL_VALLOC_PAGES * PAGESIZE;
     VirtualEnd = VallocBump;
@@ -152,7 +163,7 @@ MmVmInit(VOID)
 
         PhysicalBase = PFN_TO_ADDRESS(Pfn);
         Status = HalMmuMapPage(
-            &VasCurrent,
+            &KVas,
             VirtualStart + Off,
             PhysicalBase,
             PAGE_READ| PAGE_WRITE,