feat: add Virtual Memory Manager and Virtual Memory Area management

1 files changed, 181 insertions, 0 deletions

diff --git a/na/mm/vma.cc b/na/mm/vma.cc
new file mode 100644
index 0000000..d05a662
--- /dev/null
+++ b/na/mm/vma.cc
@@ -0,0 +1,181 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * vma.cc — Virtual Memory Area management (MI layer)
+ *
+ * Manages user address spaces using a red-black tree of VMA regions.
+ * Implements demand paging: vmm_map_user records intent only;
+ * physical pages are allocated on page fault via vmm_handle_page_fault.
+ *
+ * MI/MD separation: this file NEVER references pmap::PTE_* constants.
+ * Permission translation is delegated to pmap::vm_perm_to_pte().
+ *
+ * Reference: docs/specs/vmm.md
+ */
+
+#include <lume/vmm.h>
+#include <lume/addr.h>
+#include <lume/config.h>
+#include <lume/errno.h>
+#include <lume/pmm.h>
+#include <lume/new.h>
+#include <lume/panic.h>
+#include <arch/pmap.h>
+
+/* ------------------------------------------------------------------ */
+/*  Rbtree callbacks for VMA interval tree                            */
+/* ------------------------------------------------------------------ */
+
+static bool vma_less(struct rb_node* node, const struct rb_node* parent) {
+    VmAreaStruct* n = reinterpret_cast<VmAreaStruct*>(
+        reinterpret_cast<char*>(node) - __builtin_offsetof(VmAreaStruct, rb));
+    const VmAreaStruct* p = reinterpret_cast<const VmAreaStruct*>(
+        reinterpret_cast<const char*>(parent) - __builtin_offsetof(VmAreaStruct, rb));
+    return n->start < p->start;
+}
+
+static int vma_cmp(const void* key, const struct rb_node* node) {
+    uint64 addr = *static_cast<const uint64*>(key);
+    const VmAreaStruct* n = reinterpret_cast<const VmAreaStruct*>(
+        reinterpret_cast<const char*>(node) - __builtin_offsetof(VmAreaStruct, rb));
+    if (addr < n->start) return -1;
+    if (addr >= n->end) return 1;
+    return 0;
+}
+
+/* ------------------------------------------------------------------ */
+/*  VmSpace lifecycle                                                 */
+/* ------------------------------------------------------------------ */
+
+VmSpace* VmSpace::create() {
+    VmSpace* space = new VmSpace;
+    if (!space) return nullptr;
+
+    space->root_pa = pmap::create();
+    if (!space->root_pa) {
+        delete space;
+        return nullptr;
+    }
+
+    space->vma_tree = RB_ROOT;
+    space->lock.init("VmSpace");
+    return space;
+}
+
+void VmSpace::destroy() {
+    /* Drain VMA tree under lock, then release BEFORE delete this */
+    lock.acquire();
+    struct rb_node* node = rb_first(&vma_tree);
+    while (node) {
+        VmAreaStruct* vma = reinterpret_cast<VmAreaStruct*>(
+            reinterpret_cast<char*>(node) - __builtin_offsetof(VmAreaStruct, rb));
+        node = rb_next(node);
+        rb_erase(&vma->rb, &vma_tree);
+        delete vma;
+    }
+    uint64 root = root_pa;
+    lock.release();
+
+    /* Destroy hardware page tables outside the lock */
+    pmap::destroy(root);
+
+    /* Finally free VmSpace itself */
+    delete this;
+}
+
+/* ------------------------------------------------------------------ */
+/*  Public API: VMA manipulation                                      */
+/* ------------------------------------------------------------------ */
+
+int vmm_map_user(VmSpace* space, uint64 va, uint64 len, uint64 perm) {
+    if (!space) return -EINVAL;
+
+    va = page_align_down(va);
+    len = page_align_up(len);
+    if (len == 0) return 0;
+
+    VmAreaStruct* vma = new VmAreaStruct;
+    if (!vma) return -ENOMEM;
+    vma->start = va;
+    vma->end = va + len;
+    vma->perm = perm | VM_USER;  // Enforce user-mode access (MI flag)
+    vma->mm = space;
+
+    LockGuard guard(space->lock);
+    rb_add(&vma->rb, &space->vma_tree, vma_less);
+    return 0;
+}
+
+int vmm_unmap_user(VmSpace* space, uint64 va, uint64 len) {
+    if (!space) return -EINVAL;
+    va = page_align_down(va);
+    len = page_align_up(len);
+    uint64 end = va + len;
+
+    LockGuard guard(space->lock);
+    struct rb_node* node = rb_first(&space->vma_tree);
+    while (node) {
+        VmAreaStruct* vma = reinterpret_cast<VmAreaStruct*>(
+            reinterpret_cast<char*>(node) - __builtin_offsetof(VmAreaStruct, rb));
+        struct rb_node* nxt = rb_next(node);
+        if (vma->start >= va && vma->end <= end) {
+            rb_erase(node, &space->vma_tree);
+            delete vma;
+        }
+        node = nxt;
+    }
+    return 0;
+}
+
+/* ------------------------------------------------------------------ */
+/*  Page fault handler (demand paging)                                */
+/* ------------------------------------------------------------------ */
+
+int vmm_handle_page_fault(VmSpace* space, uint64 fault_addr, uint64 cause) {
+    if (!space) return -EINVAL;
+
+    uint64 aligned_addr = page_align_down(fault_addr);
+
+    LockGuard guard(space->lock);
+    struct rb_node* node = rb_find(&fault_addr, &space->vma_tree, vma_cmp);
+    if (!node) {
+        return -EFAULT;  // No VMA covers this address → segfault
+    }
+
+    VmAreaStruct* vma = reinterpret_cast<VmAreaStruct*>(
+        reinterpret_cast<char*>(node) - __builtin_offsetof(VmAreaStruct, rb));
+
+    (void)cause;  // TODO: differentiate read/write/exec faults
+
+    /* Check if page is already mapped */
+    uint64 paddr;
+    if (pmap::lookup(space->root_pa, aligned_addr, &paddr)) {
+        return 0;  // Already mapped
+    }
+
+    /* Allocate physical frame */
+    Frame* f = pmm_alloc_frame();
+    if (!f) return -ENOMEM;
+
+    uint64 pa = frame_to_pa(f);
+
+    /* Translate MI permission flags to hardware PTE bits (MD layer) */
+    uint64 pte_perm = pmap::vm_perm_to_pte(vma->perm);
+
+    if (pmap::map(space->root_pa, aligned_addr, pa, pte_perm) != 0) {
+        pmm_free_frame(f);
+        return -ENOMEM;
+    }
+
+    return 0;
+}
+
+/* ------------------------------------------------------------------ */
+/*  Fork / Clone (stub — requires COW infrastructure)                 */
+/* ------------------------------------------------------------------ */
+
+VmSpace* vmm_clone(VmSpace* parent) {
+    (void)parent;
+    return nullptr;
+}