feat: implement SV39 page table interface and operations for RISC-V architecture

2 files changed, 222 insertions, 0 deletions

diff --git a/na/arch/riscv/include/arch/pmap.h b/na/arch/riscv/include/arch/pmap.h
new file mode 100644
index 0000000..3f0b142
--- /dev/null
+++ b/na/arch/riscv/include/arch/pmap.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+#pragma once
+
+/*
+ * pmap — SV39 page table interface (MD layer)
+ *
+ * Namespace functions, zero runtime overhead.
+ * Implementation: arch/riscv/mm/pmap.cc
+ *
+ * Reference: docs/specs/vmm.md §3.2
+ */
+
+#include <lume/types.h>
+
+namespace pmap {
+
+/* PTE permission bits */
+inline constexpr uint64 PTE_V = 1ULL << 0;
+inline constexpr uint64 PTE_R = 1ULL << 1;
+inline constexpr uint64 PTE_W = 1ULL << 2;
+inline constexpr uint64 PTE_X = 1ULL << 3;
+inline constexpr uint64 PTE_U = 1ULL << 4;
+inline constexpr uint64 PTE_G = 1ULL << 5;
+inline constexpr uint64 PTE_A = 1ULL << 6;
+inline constexpr uint64 PTE_D = 1ULL << 7;
+
+uint64 create();
+void destroy(uint64 root_pa);
+int map(uint64 root_pa, uint64 va, uint64 pa, uint64 perm);
+void unmap(uint64 root_pa, uint64 va);
+bool lookup(uint64 root_pa, uint64 va, uint64* pa_out);
+void activate(uint64 root_pa);
+
+/*
+ * Translate MI-layer VM_* permission flags to hardware PTE bits.
+ * Called by vma.cc when faulting in a page.
+ */
+uint64 vm_perm_to_pte(uint64 vm_perm);
+
+} // namespace pmap
diff --git a/na/arch/riscv/mm/pmap.cc b/na/arch/riscv/mm/pmap.cc
new file mode 100644
index 0000000..afd71c5
--- /dev/null
+++ b/na/arch/riscv/mm/pmap.cc
@@ -0,0 +1,180 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * pmap.cc — SV39 page table operations (MD layer)
+ *
+ * Implements the pmap namespace interface for RISC-V SV39.
+ * 3-level page table: VPN[2] (9 bits) -> VPN[1] (9 bits) -> VPN[0] (9 bits)
+ * Each level is a 4KB page containing 512 PTEs of 8 bytes each.
+ *
+ * Address conversion: all page table operations work with physical addresses.
+ * To read/write page table entries we must convert PA to VA via pa_to_va().
+ *
+ * Reference: docs/specs/vmm.md
+ */
+
+#include <lume/types.h>
+#include <lume/addr.h>
+#include <lume/config.h>
+#include <lume/pmm.h>
+#include <lume/panic.h>
+#include <arch/mmu.h>
+
+namespace pmap {
+
+/* PTE bit definitions */
+inline constexpr uint64 PTE_V = 1ULL << 0;
+inline constexpr uint64 PTE_R = 1ULL << 1;
+inline constexpr uint64 PTE_W = 1ULL << 2;
+inline constexpr uint64 PTE_X = 1ULL << 3;
+inline constexpr uint64 PTE_U = 1ULL << 4;
+inline constexpr uint64 PTE_G = 1ULL << 5;
+inline constexpr uint64 PTE_A = 1ULL << 6;
+inline constexpr uint64 PTE_D = 1ULL << 7;
+
+/* SV39: 3 levels, 9 bits per level, 12-bit page offset */
+inline constexpr int kLevels = 3;
+inline constexpr int kPtePerPage = 512;
+
+/* Extract VPN[level] from a virtual address */
+static inline uint64 vpn(uint64 va, int level)
+{
+    return (va >> (12 + 9 * level)) & 0x1FF;
+}
+
+/* Extract PA from a PTE */
+static inline uint64 pte_to_pa(uint64 pte)
+{
+    return ((pte >> 10) & 0xFFFFFFFFFFFULL) << 12;
+}
+
+/* Create a PTE from a PA and flags */
+static inline uint64 pa_to_pte(uint64 pa, uint64 flags)
+{
+    return ((pa >> 12) << 10) | flags;
+}
+
+/* Convert PA to kernel VA for accessing page table contents */
+static inline uint64 *pa_to_ptr(uint64 pa)
+{
+    return reinterpret_cast<uint64 *>(pa_to_va(pa));
+}
+
+/* Allocate a zeroed page for a page table level.
+ * Returns PA of the new page, or 0 on failure. */
+static uint64 alloc_pt_page()
+{
+    Frame *f = pmm_alloc_frame();
+    if (!f)
+        return 0;
+    uint64 pa = frame_to_pa(f);
+    /* Zero the page */
+    uint64 *ptr = pa_to_ptr(pa);
+    for (int i = 0; i < kPtePerPage; i++)
+        ptr[i] = 0;
+    return pa;
+}
+
+uint64 create()
+{
+    return alloc_pt_page();
+}
+
+void destroy(uint64 root_pa)
+{
+    uint64 *l2 = pa_to_ptr(root_pa);
+    for (int i = 0; i < kPtePerPage; i++) {
+        if (!(l2[i] & PTE_V))
+            continue;
+        /* Non-leaf L2 entry? (no R/W/X bits = pointer to L1 table) */
+        if (!(l2[i] & (PTE_R | PTE_W | PTE_X))) {
+            uint64 l1_pa = pte_to_pa(l2[i]);
+            uint64 *l1 = pa_to_ptr(l1_pa);
+            for (int j = 0; j < kPtePerPage; j++) {
+                if (!(l1[j] & PTE_V))
+                    continue;
+                if (!(l1[j] & (PTE_R | PTE_W | PTE_X))) {
+                    /* L0 page table */
+                    uint64 l0_pa = pte_to_pa(l1[j]);
+                    pmm_free_frame(pa_to_frame(l0_pa));
+                }
+            }
+            pmm_free_frame(pa_to_frame(l1_pa));
+        }
+    }
+    pmm_free_frame(pa_to_frame(root_pa));
+}
+
+int map(uint64 root_pa, uint64 va, uint64 pa, uint64 perm)
+{
+    uint64 *table = pa_to_ptr(root_pa);
+
+    /* Walk levels 2 -> 1, creating intermediate tables as needed */
+    for (int level = 2; level > 0; level--) {
+        uint64 idx = vpn(va, level);
+        if (!(table[idx] & PTE_V)) {
+            uint64 child_pa = alloc_pt_page();
+            if (!child_pa)
+                return -12; /* -ENOMEM */
+            table[idx] = pa_to_pte(child_pa, PTE_V);
+        }
+        table = pa_to_ptr(pte_to_pa(table[idx]));
+    }
+
+    /* Level 0: install the leaf PTE */
+    uint64 idx = vpn(va, 0);
+    table[idx] = pa_to_pte(pa, perm | PTE_V | PTE_A | PTE_D);
+    return 0;
+}
+
+void unmap(uint64 root_pa, uint64 va)
+{
+    uint64 *table = pa_to_ptr(root_pa);
+    for (int level = 2; level > 0; level--) {
+        uint64 idx = vpn(va, level);
+        if (!(table[idx] & PTE_V))
+            return;
+        table = pa_to_ptr(pte_to_pa(table[idx]));
+    }
+    table[vpn(va, 0)] = 0;
+}
+
+bool lookup(uint64 root_pa, uint64 va, uint64 *pa_out)
+{
+    uint64 *table = pa_to_ptr(root_pa);
+    for (int level = 2; level >= 0; level--) {
+        uint64 idx = vpn(va, level);
+        uint64 pte = table[idx];
+        if (!(pte & PTE_V))
+            return false;
+        /* Leaf PTE? (has R, W, or X) */
+        if (pte & (PTE_R | PTE_W | PTE_X)) {
+            if (pa_out)
+                *pa_out = pte_to_pa(pte);
+            return true;
+        }
+        table = pa_to_ptr(pte_to_pa(pte));
+    }
+    return false;
+}
+
+void activate(uint64 root_pa)
+{
+    arch::mmu::set_page_table(root_pa);
+    arch::mmu::flush_tlb_all();
+}
+
+uint64 vm_perm_to_pte(uint64 vm_perm)
+{
+    /* Translate MI VM_* flags to SV39 PTE bits.
+     * The MI flags are defined in <lume/vmm.h>. */
+    uint64 pte = PTE_V | PTE_A | PTE_D;  // Valid + Accessed + Dirty (avoid HW A/D faults)
+    if (vm_perm & (1ULL << 0)) pte |= PTE_R;  // VM_READ
+    if (vm_perm & (1ULL << 1)) pte |= PTE_W;  // VM_WRITE
+    if (vm_perm & (1ULL << 2)) pte |= PTE_X;  // VM_EXEC
+    if (vm_perm & (1ULL << 3)) pte |= PTE_U;  // VM_USER
+    return pte;
+}
+
+} // namespace pmap