add support for multiple types of MMU

src/main.zig

@@ -54,13 +54,16 @@ export fn kmain(hartid: u64, fdt_ptr: *const anyopaque) callconv(.c) noreturn {
     debug.print("memory allocator initialized.\n", .{});
 
     const allocator = buddy.allocator();
+    const mmu_type = fdt.mmuType();
 
     var table = isa.PageTable.init(allocator) catch { @panic("Unable to create page table.\n"); };
-    table.identityMap(allocator, memory_end) catch {};
+    table.identityMap(allocator, memory_end, mmu_type) catch {};
-    table.map(allocator, @intFromPtr(console.mmio), @intFromPtr(console.mmio), .{.read = 1, .write = 1, .execute = 1}) catch {};
+    table.map(allocator, @intFromPtr(console.mmio), @intFromPtr(console.mmio), .{.read = 1, .write = 1, .execute = 1}, mmu_type) catch {
+
+    };
     isa.write_satp(.{
         .ppn = @as(u44, @intCast(@intFromPtr(table) >> 12)),
-        .mode = .sv57,
+        .mode = mmu_type,
     });
     debug.print("loaded kernel page table.\n", .{});
 

src/riscv/PageTable.zig

@@ -2,6 +2,7 @@ const std = @import("std");
 const Allocator = std.mem.Allocator;
 const PageTable = @This();
 const debug = @import("../debug.zig");
+const isa = @import("isa.zig");
 
 const MEMORY_START = @extern([*]u8, .{.name = "__memory_start"});
 
@@ -34,7 +35,7 @@ pub fn init(allocator: Allocator) !*PageTable {
     return table;
 }
 
-pub fn identityMap(self: *PageTable, allocator: Allocator, memory_end: u64) !void {
+pub fn identityMap(self: *PageTable, allocator: Allocator, memory_end: u64, mode: isa.Satp.Mode) !void {
     const flags = EntryFlags{
         .valid = 1,
         .read = 1,
@@ -45,17 +46,24 @@ pub fn identityMap(self: *PageTable, allocator: Allocator, memory_end: u64) !voi
 
     var addr: u64 = 0x0;
     while (addr < memory_end) : (addr += 0x1000) {
-        try self.map(allocator, addr, addr, flags);
+        try self.map(allocator, addr, addr, flags, mode);
     }
 }
 
-pub fn map(self: *PageTable, allocator: Allocator, virtual: u64, physical: u64, flags: EntryFlags) !void {
+pub fn map(self: *PageTable, allocator: Allocator, virtual: u64, physical: u64, flags: EntryFlags, mode: isa.Satp.Mode) !void {
     const PAGE_SIZE = 4096;
 
     if (virtual % PAGE_SIZE != 0 or physical % PAGE_SIZE != 0) {
         return error.AddressNotAligned;
     }
 
+    var level: usize = switch (mode) {
+        .sv39 => 2,
+        .sv48 => 3,
+        .sv57 => 4,
+        else => return error.UnsupportedMode,
+    };
+
     const vpn = [5]u64{
         (virtual >> 12) & 0x1ff,
         (virtual >> 21) & 0x1ff,
@@ -66,7 +74,6 @@ pub fn map(self: *PageTable, allocator: Allocator, virtual: u64, physical: u64,
 
     var current_table = self;
 
-    var level: usize = 4;
     while (level > 0) : (level -= 1) {
         const index = vpn[level];
         var entry = &current_table.entries[index];