diff --git a/.gitignore b/.gitignore
index 3c264194..a24ace96 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 # Generated by Cargo
 # will have compiled files and executables
-/target/
+debug/
+target/
 
 # Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
 # More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
diff --git a/src/kxos-frame/Cargo.toml b/src/kxos-frame/Cargo.toml
new file mode 100644
index 00000000..aa6b53fc
--- /dev/null
+++ b/src/kxos-frame/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "kxos-frame"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bitflags = "1.3"
\ No newline at end of file
diff --git a/src/kxos-frame/src/cpu.rs b/src/kxos-frame/src/cpu.rs
new file mode 100644
index 00000000..2c68e0e9
--- /dev/null
+++ b/src/kxos-frame/src/cpu.rs
@@ -0,0 +1,127 @@
+//! CPU.
+
+/// Defines a CPU-local variable.
+#[macro_export]
+macro_rules! cpu_local {
+    () => {
+        todo!()
+    };
+}
+
+/// Returns the number of CPUs.
+pub fn num_cpus() -> u32 {
+    todo!()
+}
+
+/// Returns the ID of this CPU.
+pub fn this_cpu() -> u32 {
+    todo!()
+}
+
+/// Cpu context, including both general-purpose registers and floating-point registers.
+#[derive(Clone, Default)]
+#[repr(C)]
+pub struct CpuContext {
+    pub gp_regs: GpRegs,
+    pub fs_base: u64,
+    pub fp_regs: FpRegs,
+}
+
+/// The general-purpose registers of CPU.
+#[derive(Clone, Copy, Debug, Default)]
+#[repr(C)]
+pub struct GpRegs {
+    pub r8: u64,
+    pub r9: u64,
+    pub r10: u64,
+    pub r11: u64,
+    pub r12: u64,
+    pub r13: u64,
+    pub r14: u64,
+    pub r15: u64,
+    pub rdi: u64,
+    pub rsi: u64,
+    pub rbp: u64,
+    pub rbx: u64,
+    pub rdx: u64,
+    pub rax: u64,
+    pub rcx: u64,
+    pub rsp: u64,
+    pub rip: u64,
+    pub rflag: u64,
+}
+
+/// The floating-point state of CPU.
+#[derive(Clone)]
+#[repr(C)]
+pub struct FpRegs {
+    //buf: Aligned<A16, [u8; 512]>,
+    is_valid: bool,
+}
+
+impl FpRegs {
+    /// Create a new instance.
+    ///
+    /// Note that a newly-created instance's floating point state is not
+    /// initialized, thus considered invalid (i.e., `self.is_valid() == false`).
+    pub fn new() -> Self {
+        //let buf = Aligned(unsafe { MaybeUninit::uninit().assume_init() });
+        //let is_valid = false;
+        //Self { buf, is_valid }
+        todo!("import aligned")
+    }
+
+    /// Save CPU's current floating pointer states into this instance.
+    pub fn save(&mut self) {
+        // unsafe {
+        //     _fxsave(self.buf.as_mut_ptr() as *mut u8);
+        // }
+        self.is_valid = true;
+    }
+
+    /// Save the floating state given by a slice of u8.
+    ///
+    /// It is the caller's responsibility to ensure that the source slice contains
+    /// data that is in xsave/xrstor format. The slice must have a length of 512 bytes.
+    ///
+    /// After calling this method, the state of the instance will be considered valid.
+    pub unsafe fn save_from_slice(&mut self, src: &[u8]) {
+        //(&mut self.buf).copy_from_slice(src);
+        //self.is_valid = true;
+    }
+
+    /// Returns whether the instance can contains data in valid xsave/xrstor format.
+    pub fn is_valid(&self) -> bool {
+        self.is_valid
+    }
+
+    /// Clear the state of the instance.
+    ///
+    /// This method does not reset the underlying buffer that contains the floating
+    /// point state; it only marks the buffer __invalid__.
+    pub fn clear(&mut self) {
+        self.is_valid = false;
+    }
+
+    /// Restore CPU's CPU floating pointer states from this instance.
+    ///
+    /// Panic. If the current state is invalid, the method will panic.
+    pub fn restore(&self) {
+        assert!(self.is_valid);
+        //unsafe { _fxrstor(self.buf.as_ptr()) };
+    }
+
+    /// Returns the floating point state as a slice.
+    ///
+    /// Note that the slice may contain garbage if `self.is_valid() == false`.
+    pub fn as_slice(&self) -> &[u8] {
+        //&*self.buf
+        todo!()
+    }
+}
+
+impl Default for FpRegs {
+    fn default() -> Self {
+        Self::new()
+    }
+}
diff --git a/src/kxos-frame/src/device/io_port.rs b/src/kxos-frame/src/device/io_port.rs
new file mode 100644
index 00000000..fc793137
--- /dev/null
+++ b/src/kxos-frame/src/device/io_port.rs
@@ -0,0 +1,38 @@
+use core::marker::PhantomData;
+
+use crate::prelude::*;
+
+/// An I/O port, representing a specific address in the I/O address of x86.
+pub struct IoPort<T> {
+    addr: u32,
+    _phantom: PhantomData<T>,
+}
+
+impl<T> IoPort<T> {
+    /// Create an I/O port.
+    ///
+    /// # Safety
+    ///
+    /// This function is marked unsafe as creating an I/O port is considered
+    /// a privileged operation.
+    pub unsafe fn new(addr: u32) -> Result<Self> {
+        todo!()
+    }
+}
+
+impl IoPort<u32> {
+    /// Get the address of this I/O port.
+    pub fn addr(&self) -> u32 {
+        todo!()
+    }
+
+    /// Read a value of `u32`.
+    pub fn read_u32(&self) -> u32 {
+        todo!()
+    }
+
+    /// Write a value of `u32`.
+    pub fn write_u32(&self, val: u32) {
+        todo!()
+    }
+}
diff --git a/src/kxos-frame/src/device/irq.rs b/src/kxos-frame/src/device/irq.rs
new file mode 100644
index 00000000..060f9e49
--- /dev/null
+++ b/src/kxos-frame/src/device/irq.rs
@@ -0,0 +1,46 @@
+use crate::prelude::*;
+
+/// An interupt request (IRQ) line.
+pub struct IrqLine {}
+
+impl IrqLine {
+    /// Acquire an interrupt request line.
+    ///
+    /// # Safety
+    ///
+    /// This function is marked unsafe as manipulating interrupt lines is
+    /// considered a dangerous operation.
+    pub unsafe fn acquire(irq_num: u32) -> Arc<Self> {
+        todo!()
+    }
+
+    /// Get the IRQ number.
+    pub fn num(&self) -> u32 {
+        todo!()
+    }
+
+    /// Register a callback that will be invoked when the IRQ is active.
+    ///
+    /// A handle to the callback is returned. Dropping the handle
+    /// automatically unregisters the callback.
+    ///
+    /// For each IRQ line, multiple callbacks may be registered.
+    pub fn on_active<F>(&self, callback: F) -> IrqCallbackHandle
+    where
+        F: Fn(&Self),
+    {
+        todo!()
+    }
+}
+
+/// The handle to a registered callback for a IRQ line.
+///
+/// When the handle is dropped, the callback will be unregistered automatically.
+#[must_use]
+pub struct IrqCallbackHandle {}
+
+impl Drop for IrqCallbackHandle {
+    fn drop(&mut self) {
+        todo!("unregister the callback")
+    }
+}
diff --git a/src/kxos-frame/src/device/mod.rs b/src/kxos-frame/src/device/mod.rs
new file mode 100644
index 00000000..837af58e
--- /dev/null
+++ b/src/kxos-frame/src/device/mod.rs
@@ -0,0 +1,7 @@
+//! Device-related APIs.
+
+mod io_port;
+mod irq;
+
+pub use self::io_port::IoPort;
+pub use self::irq::{IrqCallbackHandle, IrqLine};
diff --git a/src/kxos-frame/src/error.rs b/src/kxos-frame/src/error.rs
new file mode 100644
index 00000000..0f4d9021
--- /dev/null
+++ b/src/kxos-frame/src/error.rs
@@ -0,0 +1,8 @@
+/// The error type which is returned from the APIs of this crate.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum Error {
+    InvalidArgs,
+    NoMemory,
+    PageFault,
+    AccessDenied,
+}
diff --git a/src/kxos-frame/src/lib.rs b/src/kxos-frame/src/lib.rs
new file mode 100644
index 00000000..f29bfefb
--- /dev/null
+++ b/src/kxos-frame/src/lib.rs
@@ -0,0 +1,19 @@
+//! The framework part of KxOS.
+#![no_std]
+#![allow(dead_code)]
+#![allow(unused_variables)]
+#![feature(negative_impls)]
+
+extern crate alloc;
+
+pub mod cpu;
+pub mod device;
+mod error;
+pub mod prelude;
+pub mod task;
+pub mod timer;
+pub mod user;
+mod util;
+pub mod vm;
+
+pub use self::error::Error;
diff --git a/src/kxos-frame/src/prelude.rs b/src/kxos-frame/src/prelude.rs
new file mode 100644
index 00000000..bc93334a
--- /dev/null
+++ b/src/kxos-frame/src/prelude.rs
@@ -0,0 +1,10 @@
+//! The prelude.
+
+pub type Result<T> = core::result::Result<T, crate::error::Error>;
+
+pub(crate) use alloc::boxed::Box;
+pub(crate) use alloc::sync::Arc;
+pub(crate) use alloc::vec::Vec;
+pub(crate) use core::any::Any;
+
+pub use crate::vm::{Paddr, Vaddr};
diff --git a/src/kxos-frame/src/sync/mod.rs b/src/kxos-frame/src/sync/mod.rs
new file mode 100644
index 00000000..a9887a14
--- /dev/null
+++ b/src/kxos-frame/src/sync/mod.rs
@@ -0,0 +1,5 @@
+mod spin;
+mod wait;
+
+pub use self::spin::{SpinLock, SpinLockGuard};
+pub use self::wait::{WaitQueue};
\ No newline at end of file
diff --git a/src/kxos-frame/src/sync/spin.rs b/src/kxos-frame/src/sync/spin.rs
new file mode 100644
index 00000000..e0638add
--- /dev/null
+++ b/src/kxos-frame/src/sync/spin.rs
@@ -0,0 +1,39 @@
+/// A spin lock.
+pub struct SpinLock<T: ?Sized> {
+   val: T, 
+}
+
+impl<T> SpinLock<T> {
+    /// Creates a new spin lock.
+    pub fn new(val: T) -> Self {
+        todo!()
+    }
+
+    /// Acquire the spin lock. 
+    /// 
+    /// This method runs in a busy loop until the lock can be acquired.
+    /// After acquiring the spin lock, all interrupts are disabled.
+    pub fn lock(&self) -> SpinLockGuard<'a> {
+        todo!()
+    }
+}
+
+unsafe impl<T: ?Sized + Send> Send for SpinLock<T> {}
+unsafe impl<T: ?Sized + Send> Sync for SpinLock<T> {}
+
+/// The guard of a spin lock.
+pub struct SpinLockGuard<'a, T: ?Sized + 'a> {
+    lock: &'a SpinLock<T>
+}
+
+impl<'a, T> Deref for SpinLockGuard<'a, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        todo!()
+    }
+}
+
+impl<'a, T: ?Sized> !Send for SpinLockGuard<'a, T> {}
+
+unsafe impl<T: ?Sized + Sync> Sync for SpinLockGuard<'_, T> {}
\ No newline at end of file
diff --git a/src/kxos-frame/src/sync/wait.rs b/src/kxos-frame/src/sync/wait.rs
new file mode 100644
index 00000000..37597c19
--- /dev/null
+++ b/src/kxos-frame/src/sync/wait.rs
@@ -0,0 +1,69 @@
+/// A wait queue.
+///
+/// One may wait on a wait queue to put its executing thread to sleep.
+/// Multiple threads may be the waiters of a wait queue.
+/// Other threads may invoke the `wake`-family methods of a wait queue to
+/// wake up one or many waiter threads.
+pub struct WaitQueue {}
+
+impl WaitQueue {
+    /// Creates a new instance.
+    pub fn new() -> Self {
+        todo!()
+    }
+
+    /// Wait until some condition becomes true.
+    ///
+    /// This method takes a closure that tests a user-given condition.
+    /// The method only returns if the condition becomes true.
+    /// A waker thread should first make the condition true, then invoke the
+    /// `wake`-family method. This ordering is important to ensure that waiter
+    /// threads do not lose any wakeup notifiations.
+    ///
+    /// By taking a condition closure, this wait-wakeup mechanism becomes
+    /// more efficient and robust.
+    pub fn wait_until<F>(&self, mut cond: F)
+    where
+        F: FnMut() -> bool,
+    {
+        let waiter = Waiter::new();
+        self.enqueue(&waiter);
+        loop {
+            if (cond)() {
+                self.dequeue(&waiter);
+                return;
+            }
+            waiter.wait();
+        }
+        self.dequeue(&waiter);
+    }
+
+    /// Wake one waiter thread, if there is one.
+    pub fn wake_one(&self) {
+        todo!()
+    }
+
+    /// Wake all waiter threads.
+    pub fn wake_all(&self) {
+        todo!()
+    }
+
+    fn enqueue(&self, waiter: &Waiter) {
+        todo!()
+    }
+    fn dequeue(&self, waiter: &Waiter) {
+        todo!()
+    }
+}
+
+struct Waiter {}
+
+impl Waiter {
+    pub fn new() -> Self {
+        todo!()
+    }
+
+    pub fn wait(&self) {
+        todo!()
+    }
+}
diff --git a/src/kxos-frame/src/task/mod.rs b/src/kxos-frame/src/task/mod.rs
new file mode 100644
index 00000000..9b93c2ce
--- /dev/null
+++ b/src/kxos-frame/src/task/mod.rs
@@ -0,0 +1,7 @@
+//! Tasks are the unit of code execution.
+
+mod scheduler;
+mod task;
+
+pub use self::scheduler::{set_scheduler, Scheduler};
+pub use self::task::{Task, TaskStatus};
diff --git a/src/kxos-frame/src/task/scheduler.rs b/src/kxos-frame/src/task/scheduler.rs
new file mode 100644
index 00000000..b40c7522
--- /dev/null
+++ b/src/kxos-frame/src/task/scheduler.rs
@@ -0,0 +1,19 @@
+use crate::prelude::*;
+use crate::task::Task;
+
+/// A scheduler for tasks.
+///
+/// An implementation of scheduler can attach scheduler-related information
+/// with the `TypeMap` returned from `task.data()`.
+pub trait Scheduler {
+    fn enqueue(&self, task: Arc<Task>);
+
+    fn dequeue(&self) -> Option<Arc<Task>>;
+}
+
+/// Set the global task scheduler.
+///
+/// This must be called before invoking `Task::spawn`.
+pub fn set_scheduler(scheduler: &'static dyn Scheduler) {
+    todo!()
+}
diff --git a/src/kxos-frame/src/task/task.rs b/src/kxos-frame/src/task/task.rs
new file mode 100644
index 00000000..ef4e30ca
--- /dev/null
+++ b/src/kxos-frame/src/task/task.rs
@@ -0,0 +1,66 @@
+use crate::prelude::*;
+use crate::user::UserSpace;
+
+/// A task that executes a function to the end.
+pub struct Task {
+    func: Box<dyn FnOnce()>,
+    data: Box<dyn Any + Send + Sync>,
+    user_space: Option<UserSpace>,
+}
+
+impl Task {
+    /// Gets the current task.
+    pub fn current() -> Arc<Task> {
+        todo!()
+    }
+
+    /// Yields execution so that another task may be scheduled.
+    ///
+    /// Note that this method cannot be simply named "yield" as the name is
+    /// a Rust keyword.
+    pub fn yield_now() {
+        todo!()
+    }
+
+    /// Spawns a task that executes a function.
+    ///
+    /// Each task is associated with a per-task data and an optional user space.
+    /// If having a user space, then the task can switch to the user space to
+    /// execute user code. Multiple tasks can share a single user space.
+    pub fn spawn<F, T>(
+        task_fn: F,
+        task_data: T,
+        user_space: Option<Arc<UserSpace>>,
+    ) -> Result<Arc<Self>>
+    where
+        F: FnOnce(),
+        T: Any + Send + Sync,
+    {
+        todo!()
+    }
+
+    /// Returns the task status.
+    pub fn status(&self) -> TaskStatus {
+        todo!()
+    }
+
+    /// Returns the task data.
+    pub fn data(&self) -> &dyn Any {
+        todo!()
+    }
+
+    /// Returns the user space of this task, if it has.
+    pub fn user_space(&self) -> Option<&Arc<UserSpace>> {
+        todo!()
+    }
+}
+
+/// The status of a task.
+pub enum TaskStatus {
+    /// The task is runnable.
+    Runnable,
+    /// The task is sleeping.
+    Sleeping,
+    /// The task has exited.
+    Exited,
+}
diff --git a/src/kxos-frame/src/timer.rs b/src/kxos-frame/src/timer.rs
new file mode 100644
index 00000000..9fa3d499
--- /dev/null
+++ b/src/kxos-frame/src/timer.rs
@@ -0,0 +1,43 @@
+//! Timer.
+
+use crate::prelude::*;
+use core::time::Duration;
+
+/// A timer invokes a callback function after a specified span of time elapsed.
+///
+/// A new timer is initially inactive. Only after a timeout value is set with
+/// the `set` method can the timer become active and the callback function
+/// be triggered.
+///
+/// Timers are one-shot. If the time is out, one has to set the timer again
+/// in order to trigger the callback again.
+pub struct Timer {}
+
+impl Timer {
+    /// Creates a new instance, given a callback function.
+    pub fn new<F>(f: F) -> Result<Self>
+    where
+        F: FnMut(&Self),
+    {
+        todo!()
+    }
+
+    /// Set a timeout value.
+    ///
+    /// If a timeout value is already set, the timeout value will be refreshed.
+    pub fn set(&self, timeout: Duration) {
+        todo!()
+    }
+
+    /// Returns the remaining timeout value.
+    ///
+    /// If the timer is not set, then the remaining timeout value is zero.
+    pub fn remain(&self) -> Duration {
+        todo!()
+    }
+
+    /// Clear the timeout value.
+    pub fn clear(&self) {
+        todo!()
+    }
+}
diff --git a/src/kxos-frame/src/user.rs b/src/kxos-frame/src/user.rs
new file mode 100644
index 00000000..325fc574
--- /dev/null
+++ b/src/kxos-frame/src/user.rs
@@ -0,0 +1,105 @@
+//! User space.
+
+use crate::cpu::CpuContext;
+use crate::prelude::*;
+use crate::task::Task;
+use crate::vm::VmSpace;
+
+/// A user space.
+///
+/// Each user space has a VM address space and allows a task to execute in
+/// user mode.
+pub struct UserSpace {}
+
+impl UserSpace {
+    /// Creates a new instance.
+    ///
+    /// Each instance maintains a VM address space and the CPU state to enable
+    /// execution in the user space.
+    pub fn new(vm_space: VmSpace, cpu_ctx: CpuContext) -> Self {
+        todo!()
+    }
+
+    /// Returns the VM address space.
+    pub fn vm_space(&self) -> &VmSpace {
+        todo!()
+    }
+
+    /// Returns the user mode that is bound to the current task and user space.
+    ///
+    /// See `UserMode` on how to use it to execute user code.
+    ///
+    /// # Panic
+    ///
+    /// This method is intended to only allow each task to have at most one
+    /// instance of `UserMode` initiated. If this method is called again before
+    /// the first instance for the current task is dropped, then the method
+    /// panics.
+    pub fn user_mode(&self) -> UserMode<'_> {
+        todo!()
+    }
+}
+
+/// Code execution in the user mode.
+///
+/// This type enables executing the code in user space from a task in the kernel
+/// space safely.
+///
+/// Here is a sample code on how to use `UserMode`.
+///  
+/// ```
+/// let current = Task::current();
+/// let user_space = current.user_space()
+///     .expect("the current task is associated with a user space");
+/// let mut user_mode = user_space.user_mode();
+/// loop {
+///     // Execute in the user space until some interesting user event occurs
+///     let user_event = user_mode.execute();
+///     todo!("handle the user event, e.g., syscall");
+/// }
+/// ```
+pub struct UserMode<'a> {
+    current: Arc<Task>,
+    user_space: &'a Arc<UserSpace>,
+}
+
+// An instance of `UserMode` is bound to the current task. So it cannot be
+impl<'a> !Send for UserMode<'a> {}
+
+impl<'a> UserMode<'a> {
+    /// Starts executing in the user mode.
+    ///
+    /// The method returns for one of three possible reasons indicated by `UserEvent`.
+    /// 1. The user invokes a system call;
+    /// 2. The user triggers an exception;
+    /// 3. The user triggers a fault.
+    ///
+    /// After handling the user event and updating the user-mode CPU context,
+    /// this method can be invoked again to go back to the user space.
+    pub fn execute(&mut self) -> UserEvent {
+        todo!()
+    }
+
+    /// Returns an immutable reference the user-mode CPU context.
+    pub fn context(&self) -> &CpuContext {
+        todo!()
+    }
+
+    /// Returns a mutable reference the user-mode CPU context.
+    pub fn context_mut(&mut self) -> &mut CpuContext {
+        todo!()
+    }
+}
+
+/// A user event is what brings back the control of the CPU back from
+/// the user space to the kernel space.
+///
+/// Note that hardware interrupts are not considered user events as they
+/// are triggered by devices and not visible to user programs.
+/// To handle interrupts, one should register callback funtions for
+/// IRQ lines (`IrqLine`).
+pub enum UserEvent {
+    Syscall,
+    Exception,
+    Fault,
+}
diff --git a/src/kxos-frame/src/util/mod.rs b/src/kxos-frame/src/util/mod.rs
new file mode 100644
index 00000000..2c7c6017
--- /dev/null
+++ b/src/kxos-frame/src/util/mod.rs
@@ -0,0 +1,3 @@
+mod type_map;
+
+pub use self::type_map::TypeMap;
diff --git a/src/kxos-frame/src/util/type_map.rs b/src/kxos-frame/src/util/type_map.rs
new file mode 100644
index 00000000..e998fb5f
--- /dev/null
+++ b/src/kxos-frame/src/util/type_map.rs
@@ -0,0 +1,26 @@
+/// A type map is a collection whose keys are types, rather than values.
+pub struct TypeMap {}
+
+pub trait Any: core::any::Any + Send + Sync {}
+
+impl TypeMap {
+    /// Creates an empty typed map.
+    pub fn new() -> Self {
+        todo!()
+    }
+
+    /// Inserts a new item of type `T`.
+    pub fn insert<T: Any>(&mut self, val: T) -> Option<T> {
+        todo!()
+    }
+
+    /// Gets an item of type `T`.
+    pub fn get<T: Any>(&self) -> Option<&T> {
+        todo!()
+    }
+
+    /// Gets an item of type `T`.
+    pub fn remove<T: Any>(&self) -> Option<T> {
+        todo!()
+    }
+}
diff --git a/src/kxos-frame/src/vm/frame.rs b/src/kxos-frame/src/vm/frame.rs
new file mode 100644
index 00000000..2e207870
--- /dev/null
+++ b/src/kxos-frame/src/vm/frame.rs
@@ -0,0 +1,172 @@
+use core::iter::Iterator;
+
+use crate::prelude::*;
+
+/// A collection of page frames (physical memory pages).
+///
+/// For the most parts, `VmFrameVec` is like `Vec<VmFrame>`. But the
+/// implementation may or may not be based on `Vec`. Having a dedicated
+/// type to represent a series of page frames is convenient because,
+/// more often than not, one needs to operate on a batch of frames rather
+/// a single frame.
+pub struct VmFrameVec(Vec<VmFrame>);
+
+impl VmFrameVec {
+    /// Allocate a collection of free frames according to the given options.
+    ///
+    /// All returned frames are safe to use in the sense that they are
+    /// not _typed memory_. We define typed memory as the memory that
+    /// may store Rust objects or affect Rust memory safety, e.g.,
+    /// the code and data segments of the OS kernel, the stack and heap
+    /// allocated for the OS kernel.
+    ///
+    /// For more information, see `VmAllocOptions`.
+    pub fn allocate(options: &VmAllocOptions) -> Result<Self> {
+        todo!()
+    }
+
+    /// Pushs a new frame to the collection.
+    pub fn push(&mut self, new_frame: VmFrame) {
+        todo!()
+    }
+
+    /// Pop a frame from the collection.
+    pub fn pop(&mut self) -> Option<VmFrame> {
+        todo!()
+    }
+
+    /// Removes a frame at a position.
+    pub fn remove(&mut self, at: usize) -> VmFrame {
+        todo!()
+    }
+
+    /// Append some frames.
+    pub fn append(&mut self, more: VmFrameVec) -> Result<()> {
+        todo!()
+    }
+
+    /// Truncate some frames.
+    ///
+    /// If `new_len >= self.len()`, then this method has no effect.
+    pub fn truncate(&mut self, new_len: usize) {
+        todo!()
+    }
+
+    /// Returns an iterator
+    pub fn iter(&self) -> VmFrameVecIter<'_> {
+        todo!()
+    }
+
+    /// Returns the number of frames.
+    pub fn len(&self) -> usize {
+        todo!()
+    }
+
+    /// Returns the number of bytes.
+    ///
+    /// This method is equivalent to `self.len() * PAGE_SIZE`.
+    pub fn nbytes(&self) -> usize {
+        todo!()
+    }
+}
+
+/// An iterator for frames.
+pub struct VmFrameVecIter<'a> {
+    frames: &'a VmFrameVec,
+    // more...
+}
+
+impl<'a> Iterator for VmFrameVecIter<'a> {
+    type Item = &'a VmFrame;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        todo!()
+    }
+}
+
+/// Options for allocating physical memory pages (or frames).
+/// See `VmFrameVec::alloc`.
+pub struct VmAllocOptions {}
+
+impl VmAllocOptions {
+    /// Creates new options for allocating the specified number of frames.
+    pub fn new(len: usize) -> Self {
+        todo!()
+    }
+
+    /// Sets the physical address of the first frame.
+    ///
+    /// If the physical address is given, then the allocated frames will be
+    /// contiguous.
+    ///
+    /// The default value is `None`.
+    pub fn paddr(&mut self, paddr: Option<Paddr>) -> &mut Self {
+        todo!()
+    }
+
+    /// Sets whether the allocated frames should be contiguous.
+    ///
+    /// If the physical address is set, then the frames must be contiguous.
+    ///
+    /// The default value is `false`.
+    pub fn is_contiguous(&mut self, is_contiguous: bool) -> &mut Self {
+        todo!()
+    }
+
+    /// Sets whether the pages can be accessed by devices through
+    /// Direct Memory Access (DMA).
+    ///
+    /// In a TEE environment, DMAable pages are untrusted pages shared with
+    /// the VMM.
+    pub fn can_dma(&mut self, can_dma: bool) -> &mut Self {
+        todo!()
+    }
+}
+
+/// A handle to a page frame.
+///
+/// An instance of `VmFrame` is a handle to a page frame (a physical memory
+/// page). A cloned `VmFrame` refers to the same page frame as the original.
+/// As the original and cloned instances point to the same physical address,  
+/// they are treated as equal to each other. Behind the scene,
+/// a reference counter is maintained for each page frame so that
+/// when all instances of `VmFrame` that refer to the
+/// same page frame are dropped, the page frame will be freed.
+/// Free page frames are allocated in bulk by `VmFrameVec::allocate`.
+pub struct VmFrame {}
+
+impl VmFrame {
+    /// Creates a new VmFrame.
+    ///
+    /// # Safety
+    ///
+    /// The given physical address must be valid for use.
+    pub(crate) unsafe fn new(paddr: Paddr) -> Self {
+        todo!()
+    }
+
+    /// Returns the physical address of the page frame.
+    pub fn paddr(&self) -> Paddr {
+        todo!()
+    }
+
+    /// Returns whether the page frame is accessible by DMA.
+    ///
+    /// In a TEE environment, DMAable pages are untrusted pages shared with
+    /// the VMM.
+    pub fn can_dma(&self) -> bool {
+        todo!()
+    }
+}
+
+impl Clone for VmFrame {
+    fn clone(&self) -> Self {
+        todo!("inc ref cnt")
+    }
+}
+
+impl Drop for VmFrame {
+    fn drop(&mut self) {
+        todo!("dec ref cnt and if zero, free the page frame")
+    }
+}
diff --git a/src/kxos-frame/src/vm/io.rs b/src/kxos-frame/src/vm/io.rs
new file mode 100644
index 00000000..c447d3a7
--- /dev/null
+++ b/src/kxos-frame/src/vm/io.rs
@@ -0,0 +1,64 @@
+use crate::prelude::*;
+use crate::vm::Pod;
+
+/// A trait that enables reading/writing data from/to a VM object,
+/// e.g., `VmSpace`, `VmFrameVec`, and `VmFrame`.
+///
+/// # Concurrency
+///
+/// The methods may be executed by multiple concurrent reader and writer
+/// threads. In this case, if the results of concurrent reads or writes
+/// desire predictability or atomicity, the users should add extra mechanism
+/// for such properties.
+pub trait VmIo: Send + Sync {
+    /// Read a specified number of bytes at a specified offset into a given buffer.
+    ///
+    /// # No short reads
+    ///
+    /// On success, the output `buf` must be filled with the requested data
+    /// completely. If, for any reason, the requested data is only partially
+    /// available, then the method shall return an error.
+    fn read_bytes(&self, offset: usize, buf: &mut [u8]) -> Result<()>;
+
+    /// Read a value of a specified type at a specified offset.
+    fn read_val<T: Pod>(&self, offset: usize) -> Result<T> {
+        let mut val = T::new_uninit();
+        self.read_bytes(offset, val.as_bytes_mut())?;
+        Ok(val)
+    }
+
+    /// Read a slice of a specified type at a specified offset.
+    ///
+    /// # No short reads
+    ///
+    /// Similar to `read_bytes`.
+    fn read_slice<T: Pod>(&self, offset: usize, slice: &mut [T]) -> Result<()> {
+        let buf = unsafe { core::mem::transmute(slice) };
+        self.read_bytes(offset, buf)
+    }
+
+    /// Write a specified number of bytes from a given buffer at a specified offset.
+    ///
+    /// # No short writes
+    ///
+    /// On success, the input `buf` must be written to the VM object entirely.
+    /// If, for any reason, the input data can only be written partially,
+    /// then the method shall return an error.
+    fn write_bytes(&self, offset: usize, buf: &[u8]) -> Result<()>;
+
+    /// Write a value of a specified type at a specified offset.
+    fn write_val<T: Pod>(&self, offset: usize, new_val: &T) -> Result<()> {
+        self.write_bytes(offset, new_val.as_bytes())?;
+        Ok(())
+    }
+
+    /// Write a slice of a specified type at a specified offset.
+    ///
+    /// # No short write
+    ///
+    /// Similar to `write_bytes`.
+    fn write_slice<T: Pod>(&self, offset: usize, slice: &[T]) -> Result<()> {
+        let buf = unsafe { core::mem::transmute(slice) };
+        self.write_bytes(offset, buf)
+    }
+}
diff --git a/src/kxos-frame/src/vm/mod.rs b/src/kxos-frame/src/vm/mod.rs
new file mode 100644
index 00000000..7a0362c7
--- /dev/null
+++ b/src/kxos-frame/src/vm/mod.rs
@@ -0,0 +1,20 @@
+//! Virtual memory (VM).
+
+/// Virtual addresses.
+pub type Vaddr = usize;
+
+/// Physical addresses.
+pub type Paddr = usize;
+
+/// The size of a VM page or a page frame.
+pub const PAGE_SIZE: usize = 0x1000; // 4KB
+
+mod frame;
+mod io;
+mod pod;
+mod space;
+
+pub use self::frame::{VmAllocOptions, VmFrame, VmFrameVec, VmFrameVecIter};
+pub use self::io::VmIo;
+pub use self::pod::Pod;
+pub use self::space::{VmMapOptions, VmPerm, VmSpace};
diff --git a/src/kxos-frame/src/vm/pod.rs b/src/kxos-frame/src/vm/pod.rs
new file mode 100644
index 00000000..d65826fa
--- /dev/null
+++ b/src/kxos-frame/src/vm/pod.rs
@@ -0,0 +1,60 @@
+use core::mem::MaybeUninit;
+
+/// A marker trait for plain old data (POD).
+///
+/// A POD type `T:Pod` supports converting to and from arbitrary
+/// `mem::size_of::<T>()` bytes _safely_.
+/// For example, simple primitive types like `u8` and `i16`
+/// are POD types. But perhaps surprisingly, `bool` is not POD
+/// because Rust compiler makes implicit assumption that
+/// a byte of `bool` has a value of either `0` or `1`.
+/// Interpreting a byte of value `3` has a `bool` value has
+/// undefined behavior.
+///
+/// # Safety
+///
+/// Marking a non-POD type as POD may cause undefined behaviors.
+pub unsafe trait Pod: Copy + Sized {
+    /// Creates a new instance of Pod type that is filled with zeroes.
+    fn new_zeroed() -> Self {
+        // SAFETY. An all-zero value of `T: Pod` is always valid.
+        unsafe { core::mem::zeroed() }
+    }
+
+    /// Creates a new instance of Pod type with uninitialized content.
+    fn new_uninit() -> Self {
+        // SAFETY. A value of `T: Pod` can have arbitrary bits.
+        unsafe { MaybeUninit::uninit().assume_init() }
+    }
+
+    /// Creates a new instance from the given bytes.
+    fn from_bytes(bytes: &[u8]) -> Self {
+        let mut new_self = Self::new_uninit();
+        new_self.as_bytes_mut().copy_from_slice(bytes);
+        new_self
+    }
+
+    /// As a slice of bytes.
+    fn as_bytes(&self) -> &[u8] {
+        let ptr = self as *const Self as *const u8;
+        let len = core::mem::size_of::<Self>();
+        unsafe { core::slice::from_raw_parts(ptr, len) }
+    }
+
+    /// As a mutable slice of bytes.
+    fn as_bytes_mut(&mut self) -> &mut [u8] {
+        let ptr = self as *mut Self as *mut u8;
+        let len = core::mem::size_of::<Self>();
+        unsafe { core::slice::from_raw_parts_mut(ptr, len) }
+    }
+}
+
+macro_rules! impl_pod_for {
+    ($($token:tt)*/* define the input */) => {
+        /* define the expansion */
+    };
+}
+
+impl_pod_for!(u8, u16, u32, u64, i8, i16, i32, i64,);
+
+//unsafe impl<T: Pod, const N> [T; N] for Pod {}
diff --git a/src/kxos-frame/src/vm/space.rs b/src/kxos-frame/src/vm/space.rs
new file mode 100644
index 00000000..f7d99bee
--- /dev/null
+++ b/src/kxos-frame/src/vm/space.rs
@@ -0,0 +1,112 @@
+use bitflags::bitflags;
+use core::ops::Range;
+
+use crate::prelude::*;
+use crate::vm::VmFrameVec;
+
+/// Virtual memory space.
+///
+/// A virtual memory space (`VmSpace`) can be created and assigned to a user space so that
+/// the virtual memory of the user space can be manipulated safely. For example,
+/// given an arbitrary user-space pointer, one can read and write the memory
+/// location refered to by the user-space pointer without the risk of breaking the
+/// memory safety of the kernel space.
+///
+/// A newly-created `VmSpace` is not backed by any physical memory pages.
+/// To provide memory pages for a `VmSpace`, one can allocate and map
+/// physical memory (`VmFrames`) to the `VmSpace`.
+pub struct VmSpace {}
+
+impl VmSpace {
+    /// Creates a new VM address space.
+    pub fn new() -> Self {
+        todo!()
+    }
+
+    /// Maps some physical memory pages into the VM space according to the given
+    /// options, returning the address where the mapping is created.
+    ///
+    /// For more information, see `VmMapOptions`.
+    pub fn map(&self, frames: VmFrameVec, options: &VmMapOptions) -> Result<Vaddr> {
+        todo!()
+    }
+
+    /// Unmaps the physical memory pages within the VM address range.
+    ///
+    /// The range is allowed to contain gaps, where no physical memory pages
+    /// are mapped.
+    pub fn unmap(&self, range: &Range<Vaddr>) -> Result<()> {
+        todo!()
+    }
+
+    /// Update the VM protection permissions within the VM address range.
+    ///
+    /// The entire specified VM range must have been mapped with physical
+    /// memory pages.
+    pub fn protect(&self, range: &Range<Vaddr>, perm: VmPerm) -> Result<()> {
+        todo!()
+    }
+}
+
+/// Options for mapping physical memory pages into a VM address space.
+/// See `VmSpace::map`.
+pub struct VmMapOptions {}
+
+impl VmMapOptions {
+    /// Creates the default options.
+    pub fn new() -> Self {
+        todo!()
+    }
+
+    /// Sets the alignment of the address of the mapping.
+    ///
+    /// The alignment must be a power-of-2 and greater than or equal to the
+    /// page size.
+    ///
+    /// The default value of this option is the page size.
+    pub fn align(&mut self, align: usize) -> &mut Self {
+        todo!()
+    }
+
+    /// Sets the permissions of the mapping, which affects whether
+    /// the mapping can be read, written, or executed.
+    ///
+    /// The default value of this option is read-only.
+    pub fn perm(&mut self, perm: VmPerm) -> &mut Self {
+        todo!()
+    }
+
+    /// Sets the address of the new mapping.
+    ///
+    /// The default value of this option is `None`.
+    pub fn addr(&mut self, addr: Option<Vaddr>) -> &mut Self {
+        todo!()
+    }
+
+    /// Sets whether the mapping can overwrite any existing mappings.
+    ///
+    /// If this option is `true`, then the address option must be `Some(_)`.
+    ///
+    /// The default value of this option is `false`.
+    pub fn can_overwrite(&mut self, can_overwrite: bool) -> &mut Self {
+        todo!()
+    }
+}
+
+bitflags! {
+    /// Virtual memory protection permissions.
+    pub struct VmPerm: u8 {
+        /// Readable.
+        const R = 0b00000001;
+        /// Writable.
+        const W = 0b00000010;
+        /// Executable.
+        const X = 0b00000100;
+        /// Readable + writable.
+        const RW = Self::R.bits | Self::W.bits;
+        /// Readable + execuable.
+        const RX = Self::R.bits | Self::X.bits;
+        /// Readable + writable + executable.
+        const RWX = Self::R.bits | Self::W.bits | Self::X.bits;
+    }
+}
diff --git a/src/rust-toolchain.toml b/src/rust-toolchain.toml
new file mode 100644
index 00000000..725abbe3
--- /dev/null
+++ b/src/rust-toolchain.toml
@@ -0,0 +1,2 @@
+[toolchain]
+channel = "nightly-2022-08-01"
\ No newline at end of file