diff --git a/src/kern/cpu.zig b/src/kern/cpu.zig
index 1401ae9..ee672a5 100644
--- a/src/kern/cpu.zig
+++ b/src/kern/cpu.zig
@@ -1,6 +1,7 @@
 const std = @import("std");
 const rtl = @import("rtl");
 const b = @import("base");
+const config = @import("config");
 const ke = b.ke;
 const ki = b.ke.private;
 
@@ -89,3 +90,44 @@ pub fn CpuLocal(comptime T: type, comptime init: T) type {
         }
     };
 }
+
+/// Bitmask of CPUs.
+pub const CpuMask = struct {
+    const bits_per_word = @sizeOf(usize) * 8;
+    const num_words = (config.CONFIG_NCPUS + bits_per_word - 1) / bits_per_word;
+
+    bits: [num_words]usize,
+
+    /// Return an empty `CpuMask`.
+    pub fn empty() CpuMask {
+        return CpuMask{ .bits = [_]usize{0} ** num_words };
+    }
+
+    /// Set the bit corresponding to `cpu_id`.
+    pub fn set(self: *CpuMask, cpu_id: usize) void {
+        const word_index = cpu_id / bits_per_word;
+        const bit_index = cpu_id % bits_per_word;
+        self.bits[word_index] |= (@as(usize, 1) << @intCast(bit_index));
+    }
+
+    /// Clear the bit corresponding to `cpu_id`.
+    pub fn clear(self: *CpuMask, cpu_id: usize) void {
+        const word_index = cpu_id / bits_per_word;
+        const bit_index = cpu_id % bits_per_word;
+        self.bits[word_index] &= ~(@as(usize, 1) << @intCast(bit_index));
+    }
+
+    /// Check whether the bit corresponding to `cpu_id` is set.
+    pub fn is_set(self: *const CpuMask, cpu_id: usize) bool {
+        const word_index = cpu_id / bits_per_word;
+        const bit_index = cpu_id % bits_per_word;
+        return (self.bits[word_index] & (@as(usize, 1) << @intCast(bit_index))) != 0;
+    }
+
+    pub fn is_full(self: *const CpuMask) bool {
+        for (self.bits) |word| {
+            if (word != std.math.maxInt(usize)) return false;
+        }
+        return true;
+    }
+};
diff --git a/src/kern/root.zig b/src/kern/root.zig
index 3417576..fb710c3 100644
--- a/src/kern/root.zig
+++ b/src/kern/root.zig
@@ -54,6 +54,7 @@ pub const wait = struct {
 
 pub const Cpu = p.cpu.Cpu;
 pub const CpuLocal = p.cpu.CpuLocal;
+pub const CpuMask = p.cpu.CpuMask;
 
 comptime {
     if (!@hasDecl(p.impl, "curcpu")) @compileError("impl must provide curcpu()");