diff --git a/crate/memory/src/memory_set/handler/byframe.rs b/crate/memory/src/memory_set/handler/byframe.rs
index d824969..89b45cc 100644
--- a/crate/memory/src/memory_set/handler/byframe.rs
+++ b/crate/memory/src/memory_set/handler/byframe.rs
@@ -13,7 +13,6 @@ impl<T: FrameAllocator> MemoryHandler for ByFrame<T> {
     fn map(&self, pt: &mut PageTable, addr: VirtAddr, attr: &MemoryAttr) {
         let target = self.allocator.alloc().expect("failed to allocate frame");
         let entry = pt.map(addr, target);
-        entry.set_present(true);
         attr.apply(entry);
     }
 
diff --git a/crate/memory/src/memory_set/handler/linear.rs b/crate/memory/src/memory_set/handler/linear.rs
index d727166..a3c8bab 100644
--- a/crate/memory/src/memory_set/handler/linear.rs
+++ b/crate/memory/src/memory_set/handler/linear.rs
@@ -13,7 +13,6 @@ impl MemoryHandler for Linear {
     fn map(&self, pt: &mut PageTable, addr: VirtAddr, attr: &MemoryAttr) {
         let target = (addr as isize + self.offset) as PhysAddr;
         let entry = pt.map(addr, target);
-        entry.set_present(true);
         attr.apply(entry);
     }
 
diff --git a/crate/memory/src/memory_set/mod.rs b/crate/memory/src/memory_set/mod.rs
index 3b75a91..63c9946 100644
--- a/crate/memory/src/memory_set/mod.rs
+++ b/crate/memory/src/memory_set/mod.rs
@@ -48,24 +48,14 @@ impl MemoryArea {
     pub fn contains(&self, addr: VirtAddr) -> bool {
         addr >= self.start_addr && addr < self.end_addr
     }
-    /// Check the pointer is within the readable memory
-    pub fn check_ptr<T>(&self, ptr: *const T) -> bool {
-        self.check_array(ptr, 1)
-    }
-    /// Check the pointer is within the writable memory
-    pub fn check_mut_ptr<T>(&self, ptr: *mut T) -> bool {
-        self.check_mut_array(ptr, 1)
-    }
     /// Check the array is within the readable memory
-    pub fn check_array<S>(&self, ptr: *const S, count: usize) -> bool {
+    fn check_read_array<S>(&self, ptr: *const S, count: usize) -> bool {
         ptr as usize >= self.start_addr &&
-            unsafe { ptr.offset(count as isize) as usize } <= self.end_addr
+            unsafe { ptr.add(count) as usize } <= self.end_addr
     }
     /// Check the array is within the writable memory
-    pub fn check_mut_array<S>(&self, ptr: *mut S, count: usize) -> bool {
-        !self.attr.readonly &&
-            ptr as usize >= self.start_addr &&
-            unsafe { ptr.offset(count as isize) as usize } <= self.end_addr
+    fn check_write_array<S>(&self, ptr: *mut S, count: usize) -> bool {
+        !self.attr.readonly && self.check_read_array(ptr, count)
     }
     /// Check the null-end C string is within the readable memory, and is valid.
     /// If so, clone it to a String.
@@ -207,27 +197,23 @@ impl<T: InactivePageTable> MemorySet<T> {
         }
     }
     /// Check the pointer is within the readable memory
-    pub fn check_ptr<S>(&self, ptr: *const S) -> VMResult<()> {
-        self.areas.iter()
-            .find(|area| area.check_ptr(ptr))
-            .map(|_|()).ok_or(VMError::InvalidPtr)
+    pub fn check_read_ptr<S>(&self, ptr: *const S) -> VMResult<()> {
+        self.check_read_array(ptr, 1)
     }
     /// Check the pointer is within the writable memory
-    pub fn check_mut_ptr<S>(&self, ptr: *mut S) -> VMResult<()> {
-        self.areas.iter()
-            .find(|area| area.check_mut_ptr(ptr))
-            .map(|_|()).ok_or(VMError::InvalidPtr)
+    pub fn check_write_ptr<S>(&self, ptr: *mut S) -> VMResult<()> {
+        self.check_write_array(ptr, 1)
     }
     /// Check the array is within the readable memory
-    pub fn check_array<S>(&self, ptr: *const S, count: usize) -> VMResult<()> {
+    pub fn check_read_array<S>(&self, ptr: *const S, count: usize) -> VMResult<()> {
         self.areas.iter()
-            .find(|area| area.check_array(ptr, count))
+            .find(|area| area.check_read_array(ptr, count))
             .map(|_|()).ok_or(VMError::InvalidPtr)
     }
     /// Check the array is within the writable memory
-    pub fn check_mut_array<S>(&self, ptr: *mut S, count: usize) -> VMResult<()> {
+    pub fn check_write_array<S>(&self, ptr: *mut S, count: usize) -> VMResult<()> {
         self.areas.iter()
-            .find(|area| area.check_mut_array(ptr, count))
+            .find(|area| area.check_write_array(ptr, count))
             .map(|_|()).ok_or(VMError::InvalidPtr)
     }
     /// Check the null-end C string is within the readable memory, and is valid.
diff --git a/crate/memory/src/paging/mod.rs b/crate/memory/src/paging/mod.rs
index 0c7ecc1..8ce357f 100644
--- a/crate/memory/src/paging/mod.rs
+++ b/crate/memory/src/paging/mod.rs
@@ -43,23 +43,15 @@ pub trait PageTable {
         unsafe { (addr as *mut u8).write(data) }
     }
 
-    /// When 'vaddr' is not mapped, map it to 'paddr'.
+    /// When `vaddr` is not mapped, map it to `paddr`.
     fn map_if_not_exists(&mut self, vaddr: VirtAddr, paddr: usize) -> bool {
-        let entry = self.get_entry(vaddr);
-        match entry {
-            None => {
-                self.map(vaddr, paddr);
-                true
-            },
-            Some(page_table_entry) => {
-                if page_table_entry.present() {
-                    false
-                } else {
-                    self.map(vaddr, paddr);
-                    true
-                }
+        if let Some(entry) = self.get_entry(vaddr) {
+            if entry.present() {
+                return false;
             }
         }
+        self.map(vaddr, paddr);
+        true
     }
 }
 
diff --git a/kernel/src/memory.rs b/kernel/src/memory.rs
index 61229af..1adf4e2 100644
--- a/kernel/src/memory.rs
+++ b/kernel/src/memory.rs
@@ -102,7 +102,7 @@ impl Drop for KernelStack {
 #[cfg(not(feature = "no_mmu"))]
 pub fn handle_page_fault(addr: usize) -> bool {
     debug!("page fault @ {:#x}", addr);
-    process().memory_set.handle_page_fault(addr)
+    process().vm.handle_page_fault(addr)
 }
 
 pub fn init_heap() {
diff --git a/kernel/src/process/structs.rs b/kernel/src/process/structs.rs
index 06be2e0..30cd633 100644
--- a/kernel/src/process/structs.rs
+++ b/kernel/src/process/structs.rs
@@ -85,7 +85,7 @@ impl fmt::Display for Pid {
 
 pub struct Process {
     // resources
-    pub memory_set: MemorySet,
+    pub vm: MemorySet,
     pub files: BTreeMap<usize, FileLike>,
     pub cwd: String,
     futexes: BTreeMap<usize, Arc<Condvar>>,
@@ -140,7 +140,7 @@ impl Thread {
             kstack: KernelStack::new(),
             clear_child_tid: 0,
             proc: Arc::new(Mutex::new(Process {
-                memory_set: MemorySet::new(),
+                vm: MemorySet::new(),
                 files: BTreeMap::default(),
                 cwd: String::from("/"),
                 futexes: BTreeMap::default(),
@@ -156,15 +156,15 @@ impl Thread {
 
     /// Make a new kernel thread starting from `entry` with `arg`
     pub fn new_kernel(entry: extern fn(usize) -> !, arg: usize) -> Box<Thread> {
-        let memory_set = MemorySet::new();
+        let vm = MemorySet::new();
         let kstack = KernelStack::new();
         Box::new(Thread {
-            context: unsafe { Context::new_kernel_thread(entry, arg, kstack.top(), memory_set.token()) },
+            context: unsafe { Context::new_kernel_thread(entry, arg, kstack.top(), vm.token()) },
             kstack,
             clear_child_tid: 0,
             // TODO: kernel thread should not have a process
             proc: Arc::new(Mutex::new(Process {
-                memory_set,
+                vm,
                 files: BTreeMap::default(),
                 cwd: String::from("/"),
                 futexes: BTreeMap::default(),
@@ -199,7 +199,7 @@ impl Thread {
         }
 
         // Make page table
-        let (mut memory_set, entry_addr) = memory_set_from(&elf);
+        let (mut vm, entry_addr) = memory_set_from(&elf);
 
         // User stack
         use crate::consts::{USER_STACK_OFFSET, USER_STACK_SIZE, USER32_STACK_OFFSET};
@@ -209,11 +209,11 @@ impl Thread {
                 true => (USER32_STACK_OFFSET, USER32_STACK_OFFSET + USER_STACK_SIZE),
                 false => (USER_STACK_OFFSET, USER_STACK_OFFSET + USER_STACK_SIZE),
             };
-            memory_set.push(ustack_buttom, ustack_top,  MemoryAttr::default().user(), ByFrame::new(GlobalFrameAlloc), "user_stack");
+            vm.push(ustack_buttom, ustack_top,  MemoryAttr::default().user(), ByFrame::new(GlobalFrameAlloc), "user_stack");
             ustack_top
         };
         #[cfg(feature = "no_mmu")]
-        let mut ustack_top = memory_set.push(USER_STACK_SIZE).as_ptr() as usize + USER_STACK_SIZE;
+        let mut ustack_top = vm.push(USER_STACK_SIZE).as_ptr() as usize + USER_STACK_SIZE;
 
         let init_info = ProcInitInfo {
             args: args.map(|s| String::from(s)).collect(),
@@ -237,10 +237,10 @@ impl Thread {
             },
         };
         unsafe {
-            memory_set.with(|| { ustack_top = init_info.push_at(ustack_top) });
+            vm.with(|| { ustack_top = init_info.push_at(ustack_top) });
         }
 
-        trace!("{:#x?}", memory_set);
+        trace!("{:#x?}", vm);
 
         let kstack = KernelStack::new();
 
@@ -252,12 +252,12 @@ impl Thread {
         Box::new(Thread {
             context: unsafe {
                 Context::new_user_thread(
-                    entry_addr, ustack_top, kstack.top(), is32, memory_set.token())
+                    entry_addr, ustack_top, kstack.top(), is32, vm.token())
             },
             kstack,
             clear_child_tid: 0,
             proc: Arc::new(Mutex::new(Process {
-                memory_set,
+                vm,
                 files,
                 cwd: String::from("/"),
                 futexes: BTreeMap::default(),
@@ -274,18 +274,18 @@ impl Thread {
     /// Fork a new process from current one
     pub fn fork(&self, tf: &TrapFrame) -> Box<Thread> {
         // Clone memory set, make a new page table
-        let memory_set = self.proc.lock().memory_set.clone();
+        let vm = self.proc.lock().vm.clone();
         let files = self.proc.lock().files.clone();
         let cwd = self.proc.lock().cwd.clone();
         let parent = Some(self.proc.clone());
         debug!("fork: finish clone MemorySet");
 
         // MMU:   copy data to the new space
-        // NoMMU: coping data has been done in `memory_set.clone()`
+        // NoMMU: coping data has been done in `vm.clone()`
         #[cfg(not(feature = "no_mmu"))]
-        for area in memory_set.iter() {
+        for area in vm.iter() {
             let data = Vec::<u8>::from(unsafe { area.as_slice() });
-            unsafe { memory_set.with(|| {
+            unsafe { vm.with(|| {
                 area.as_slice_mut().copy_from_slice(data.as_slice())
             }) }
         }
@@ -302,11 +302,11 @@ impl Thread {
 
 
         Box::new(Thread {
-            context: unsafe { Context::new_fork(tf, kstack.top(), memory_set.token()) },
+            context: unsafe { Context::new_fork(tf, kstack.top(), vm.token()) },
             kstack,
             clear_child_tid: 0,
             proc: Arc::new(Mutex::new(Process {
-                memory_set,
+                vm,
                 files,
                 cwd,
                 futexes: BTreeMap::default(),
@@ -323,7 +323,7 @@ impl Thread {
     /// Create a new thread in the same process.
     pub fn clone(&self, tf: &TrapFrame, stack_top: usize, tls: usize, clear_child_tid: usize) -> Box<Thread> {
         let kstack = KernelStack::new();
-        let token = self.proc.lock().memory_set.token();
+        let token = self.proc.lock().vm.token();
         Box::new(Thread {
             context: unsafe { Context::new_clone(tf, stack_top, kstack.top(), token, tls) },
             kstack,
diff --git a/kernel/src/syscall/custom.rs b/kernel/src/syscall/custom.rs
index d5b4a85..2894f00 100644
--- a/kernel/src/syscall/custom.rs
+++ b/kernel/src/syscall/custom.rs
@@ -24,9 +24,9 @@ pub fn sys_map_pci_device(vendor: usize, product: usize) -> SysResult {
         .ok_or(SysError::ENOENT)?;
 
     let mut proc = process();
-    let virt_addr = proc.memory_set.find_free_area(0, len);
+    let virt_addr = proc.vm.find_free_area(0, len);
     let attr = MemoryAttr::default().user();
-    proc.memory_set.push(
+    proc.vm.push(
         virt_addr,
         virt_addr + len,
         attr,
@@ -45,12 +45,12 @@ pub fn sys_map_pci_device(vendor: usize, product: usize) -> SysResult {
 /// mapped to a list of virtual addresses.
 pub fn sys_get_paddr(vaddrs: *const u64, paddrs: *mut u64, count: usize) -> SysResult {
     let mut proc = process();
-    proc.memory_set.check_array(vaddrs, count)?;
-    proc.memory_set.check_mut_array(paddrs, count)?;
+    proc.vm.check_read_array(vaddrs, count)?;
+    proc.vm.check_write_array(paddrs, count)?;
     let vaddrs = unsafe { slice::from_raw_parts(vaddrs, count) };
     let paddrs = unsafe { slice::from_raw_parts_mut(paddrs, count) };
     for i in 0..count {
-        let paddr = proc.memory_set.translate(vaddrs[i] as usize).unwrap_or(0);
+        let paddr = proc.vm.translate(vaddrs[i] as usize).unwrap_or(0);
         paddrs[i] = paddr as u64;
     }
     Ok(0)
diff --git a/kernel/src/syscall/fs.rs b/kernel/src/syscall/fs.rs
index 6f4f46f..96b11d5 100644
--- a/kernel/src/syscall/fs.rs
+++ b/kernel/src/syscall/fs.rs
@@ -17,7 +17,7 @@ pub fn sys_read(fd: usize, base: *mut u8, len: usize) -> SysResult {
         // we trust pid 0 process
         info!("read: fd: {}, base: {:?}, len: {:#x}", fd, base, len);
     }
-    proc.memory_set.check_mut_array(base, len)?;
+    proc.vm.check_write_array(base, len)?;
     match proc.files.get(&fd) {
         Some(FileLike::File(_)) => sys_read_file(&mut proc, fd, base, len),
         Some(FileLike::Socket(_)) => sys_read_socket(&mut proc, fd, base, len),
@@ -31,7 +31,7 @@ pub fn sys_write(fd: usize, base: *const u8, len: usize) -> SysResult {
         // we trust pid 0 process
         info!("write: fd: {}, base: {:?}, len: {:#x}", fd, base, len);
     }
-    proc.memory_set.check_array(base, len)?;
+    proc.vm.check_read_array(base, len)?;
 
     match proc.files.get(&fd) {
         Some(FileLike::File(_)) => sys_write_file(&mut proc, fd, base, len),
@@ -43,7 +43,7 @@ pub fn sys_write(fd: usize, base: *const u8, len: usize) -> SysResult {
 pub fn sys_pread(fd: usize, base: *mut u8, len: usize, offset: usize) -> SysResult {
     info!("pread: fd: {}, base: {:?}, len: {}, offset: {}", fd, base, len, offset);
     let mut proc = process();
-    proc.memory_set.check_mut_array(base, len)?;
+    proc.vm.check_write_array(base, len)?;
 
     let slice = unsafe { slice::from_raw_parts_mut(base, len) };
     let len = proc.get_file(fd)?.read_at(offset, slice)?;
@@ -53,7 +53,7 @@ pub fn sys_pread(fd: usize, base: *mut u8, len: usize, offset: usize) -> SysResu
 pub fn sys_pwrite(fd: usize, base: *const u8, len: usize, offset: usize) -> SysResult {
     info!("pwrite: fd: {}, base: {:?}, len: {}, offset: {}", fd, base, len, offset);
     let mut proc = process();
-    proc.memory_set.check_array(base, len)?;
+    proc.vm.check_read_array(base, len)?;
 
     let slice = unsafe { slice::from_raw_parts(base, len) };
     let len = proc.get_file(fd)?.write_at(offset, slice)?;
@@ -75,7 +75,7 @@ pub fn sys_write_file(proc: &mut Process, fd: usize, base: *const u8, len: usize
 pub fn sys_poll(ufds: *mut PollFd, nfds: usize, timeout_msecs: usize) -> SysResult {
     info!("poll: ufds: {:?}, nfds: {}, timeout_msecs: {:#x}", ufds, nfds, timeout_msecs);
     let proc = process();
-    proc.memory_set.check_mut_array(ufds, nfds)?;
+    proc.vm.check_write_array(ufds, nfds)?;
 
     let polls = unsafe { slice::from_raw_parts_mut(ufds, nfds) };
     for poll in polls.iter() {
@@ -148,11 +148,11 @@ struct FdSet {
 impl FdSet {
     /// Initialize a `FdSet` from pointer and number of fds
     /// Check if the array is large enough
-    fn new(proc: &Process, addr: *mut u32, nfds: usize) -> Result<FdSet, SysError> {
+    fn new(vm: &MemorySet, addr: *mut u32, nfds: usize) -> Result<FdSet, SysError> {
         let mut saved = [0u32; MAX_FDSET_SIZE];
         if addr as usize != 0 {
             let len = (nfds + FD_PER_ITEM - 1) / FD_PER_ITEM;
-            proc.memory_set.check_mut_array(addr, len)?;
+            vm.check_write_array(addr, len)?;
             if len > MAX_FDSET_SIZE {
                 return Err(SysError::EINVAL);
             }
@@ -199,11 +199,11 @@ pub fn sys_select(nfds: usize, read: *mut u32, write: *mut u32, err: *mut u32, t
     info!("select: nfds: {}, read: {:?}, write: {:?}, err: {:?}, timeout: {:?}", nfds, read, write, err, timeout);
 
     let proc = process();
-    let mut read_fds = FdSet::new(&proc, read, nfds)?;
-    let mut write_fds = FdSet::new(&proc, write, nfds)?;
-    let mut err_fds = FdSet::new(&proc, err, nfds)?;
+    let mut read_fds = FdSet::new(&proc.vm, read, nfds)?;
+    let mut write_fds = FdSet::new(&proc.vm, write, nfds)?;
+    let mut err_fds = FdSet::new(&proc.vm, err, nfds)?;
     let timeout_msecs = if timeout as usize != 0 {
-        proc.memory_set.check_ptr(timeout)?;
+        proc.vm.check_read_ptr(timeout)?;
         unsafe { *timeout }.to_msec()
     } else {
         // infinity
@@ -269,7 +269,7 @@ pub fn sys_select(nfds: usize, read: *mut u32, write: *mut u32, err: *mut u32, t
 pub fn sys_readv(fd: usize, iov_ptr: *const IoVec, iov_count: usize) -> SysResult {
     info!("readv: fd: {}, iov: {:?}, count: {}", fd, iov_ptr, iov_count);
     let mut proc = process();
-    let mut iovs = IoVecs::check_and_new(iov_ptr, iov_count, &proc.memory_set, true)?;
+    let mut iovs = IoVecs::check_and_new(iov_ptr, iov_count, &proc.vm, true)?;
 
     // read all data to a buf
     let mut file = proc.get_file(fd)?.clone();
@@ -284,7 +284,7 @@ pub fn sys_readv(fd: usize, iov_ptr: *const IoVec, iov_count: usize) -> SysResul
 pub fn sys_writev(fd: usize, iov_ptr: *const IoVec, iov_count: usize) -> SysResult {
     info!("writev: fd: {}, iov: {:?}, count: {}", fd, iov_ptr, iov_count);
     let mut proc = process();
-    let iovs = IoVecs::check_and_new(iov_ptr, iov_count, &proc.memory_set, false)?;
+    let iovs = IoVecs::check_and_new(iov_ptr, iov_count, &proc.vm, false)?;
 
     let buf = iovs.read_all_to_vec();
     let len = buf.len();
@@ -298,7 +298,7 @@ pub fn sys_writev(fd: usize, iov_ptr: *const IoVec, iov_count: usize) -> SysResu
 
 pub fn sys_open(path: *const u8, flags: usize, mode: usize) -> SysResult {
     let mut proc = process();
-    let path = unsafe { proc.memory_set.check_and_clone_cstr(path)? };
+    let path = unsafe { proc.vm.check_and_clone_cstr(path)? };
     let flags = OpenFlags::from_bits_truncate(flags);
     info!("open: path: {:?}, flags: {:?}, mode: {:#o}", path, flags, mode);
 
@@ -345,7 +345,7 @@ pub fn sys_access(path: *const u8, mode: usize) -> SysResult {
 pub fn sys_getcwd(buf: *mut u8, len: usize) -> SysResult {
     info!("getcwd: buf: {:?}, len: {:#x}", buf, len);
     let proc = process();
-    proc.memory_set.check_mut_array(buf, len)?;
+    proc.vm.check_write_array(buf, len)?;
     if proc.cwd.len() + 1 > len {
         return Err(SysError::ERANGE);
     }
@@ -361,9 +361,9 @@ pub fn sys_stat(path: *const u8, stat_ptr: *mut Stat) -> SysResult {
 }
 
 pub fn sys_fstat(fd: usize, stat_ptr: *mut Stat) -> SysResult {
-    info!("fstat: fd: {}", fd);
+    info!("fstat: fd: {}, stat_ptr: {:?}", fd, stat_ptr);
     let mut proc = process();
-    proc.memory_set.check_mut_ptr(stat_ptr)?;
+    proc.vm.check_write_ptr(stat_ptr)?;
     let file = proc.get_file(fd)?;
     let stat = Stat::from(file.metadata()?);
     // TODO: handle symlink
@@ -373,9 +373,9 @@ pub fn sys_fstat(fd: usize, stat_ptr: *mut Stat) -> SysResult {
 
 pub fn sys_lstat(path: *const u8, stat_ptr: *mut Stat) -> SysResult {
     let proc = process();
-    let path = unsafe { proc.memory_set.check_and_clone_cstr(path)? };
-    proc.memory_set.check_mut_ptr(stat_ptr)?;
-    info!("lstat: path: {}", path);
+    let path = unsafe { proc.vm.check_and_clone_cstr(path)? };
+    proc.vm.check_write_ptr(stat_ptr)?;
+    info!("lstat: path: {:?}, stat_ptr: {:?}", path, stat_ptr);
 
     let inode = proc.lookup_inode(&path)?;
     let stat = Stat::from(inode.metadata()?);
@@ -412,7 +412,7 @@ pub fn sys_fdatasync(fd: usize) -> SysResult {
 
 pub fn sys_truncate(path: *const u8, len: usize) -> SysResult {
     let proc = process();
-    let path = unsafe { proc.memory_set.check_and_clone_cstr(path)? };
+    let path = unsafe { proc.vm.check_and_clone_cstr(path)? };
     info!("truncate: path: {:?}, len: {}", path, len);
     proc.lookup_inode(&path)?.resize(len)?;
     Ok(0)
@@ -427,7 +427,7 @@ pub fn sys_ftruncate(fd: usize, len: usize) -> SysResult {
 pub fn sys_getdents64(fd: usize, buf: *mut LinuxDirent64, buf_size: usize) -> SysResult {
     info!("getdents64: fd: {}, ptr: {:?}, buf_size: {}", fd, buf, buf_size);
     let mut proc = process();
-    proc.memory_set.check_mut_array(buf as *mut u8, buf_size)?;
+    proc.vm.check_write_array(buf as *mut u8, buf_size)?;
     let file = proc.get_file(fd)?;
     let info = file.metadata()?;
     if info.type_ != FileType::Dir {
@@ -468,7 +468,7 @@ pub fn sys_dup2(fd1: usize, fd2: usize) -> SysResult {
 
 pub fn sys_chdir(path: *const u8) -> SysResult {
     let mut proc = process();
-    let path = unsafe { proc.memory_set.check_and_clone_cstr(path)? };
+    let path = unsafe { proc.vm.check_and_clone_cstr(path)? };
     info!("chdir: path: {:?}", path);
 
     let inode = proc.lookup_inode(&path)?;
@@ -489,8 +489,8 @@ pub fn sys_chdir(path: *const u8) -> SysResult {
 
 pub fn sys_rename(oldpath: *const u8, newpath: *const u8) -> SysResult {
     let proc = process();
-    let oldpath = unsafe { proc.memory_set.check_and_clone_cstr(oldpath)? };
-    let newpath = unsafe { proc.memory_set.check_and_clone_cstr(newpath)? };
+    let oldpath = unsafe { proc.vm.check_and_clone_cstr(oldpath)? };
+    let newpath = unsafe { proc.vm.check_and_clone_cstr(newpath)? };
     info!("rename: oldpath: {:?}, newpath: {:?}", oldpath, newpath);
 
     let (old_dir_path, old_file_name) = split_path(&oldpath);
@@ -503,7 +503,7 @@ pub fn sys_rename(oldpath: *const u8, newpath: *const u8) -> SysResult {
 
 pub fn sys_mkdir(path: *const u8, mode: usize) -> SysResult {
     let proc = process();
-    let path = unsafe { proc.memory_set.check_and_clone_cstr(path)? };
+    let path = unsafe { proc.vm.check_and_clone_cstr(path)? };
     // TODO: check pathname
     info!("mkdir: path: {:?}, mode: {:#o}", path, mode);
 
@@ -518,7 +518,7 @@ pub fn sys_mkdir(path: *const u8, mode: usize) -> SysResult {
 
 pub fn sys_rmdir(path: *const u8) -> SysResult {
     let proc = process();
-    let path = unsafe { proc.memory_set.check_and_clone_cstr(path)? };
+    let path = unsafe { proc.vm.check_and_clone_cstr(path)? };
     info!("rmdir: path: {:?}", path);
 
     let (dir_path, file_name) = split_path(&path);
@@ -533,8 +533,8 @@ pub fn sys_rmdir(path: *const u8) -> SysResult {
 
 pub fn sys_link(oldpath: *const u8, newpath: *const u8) -> SysResult {
     let proc = process();
-    let oldpath = unsafe { proc.memory_set.check_and_clone_cstr(oldpath)? };
-    let newpath = unsafe { proc.memory_set.check_and_clone_cstr(newpath)? };
+    let oldpath = unsafe { proc.vm.check_and_clone_cstr(oldpath)? };
+    let newpath = unsafe { proc.vm.check_and_clone_cstr(newpath)? };
     info!("link: oldpath: {:?}, newpath: {:?}", oldpath, newpath);
 
     let (new_dir_path, new_file_name) = split_path(&newpath);
@@ -546,7 +546,7 @@ pub fn sys_link(oldpath: *const u8, newpath: *const u8) -> SysResult {
 
 pub fn sys_unlink(path: *const u8) -> SysResult {
     let proc = process();
-    let path = unsafe { proc.memory_set.check_and_clone_cstr(path)? };
+    let path = unsafe { proc.vm.check_and_clone_cstr(path)? };
     info!("unlink: path: {:?}", path);
 
     let (dir_path, file_name) = split_path(&path);
@@ -563,7 +563,7 @@ pub fn sys_pipe(fds: *mut u32) -> SysResult {
     info!("pipe: fds: {:?}", fds);
 
     let mut proc = process();
-    proc.memory_set.check_mut_array(fds, 2)?;
+    proc.vm.check_write_array(fds, 2)?;
     let (read, write) = Pipe::create_pair();
 
     let read_fd = proc.get_free_fd();
@@ -940,16 +940,16 @@ struct IoVecs(Vec<&'static mut [u8]>);
 
 impl IoVecs {
     fn check_and_new(iov_ptr: *const IoVec, iov_count: usize, vm: &MemorySet, readv: bool) -> Result<Self, SysError> {
-        vm.check_array(iov_ptr, iov_count)?;
+        vm.check_read_array(iov_ptr, iov_count)?;
         let iovs = unsafe { slice::from_raw_parts(iov_ptr, iov_count) }.to_vec();
         // check all bufs in iov
         for iov in iovs.iter() {
             if iov.len > 0 {
                 // skip empty iov
                 if readv {
-                    vm.check_mut_array(iov.base, iov.len as usize)?;
+                    vm.check_write_array(iov.base, iov.len as usize)?;
                 } else {
-                    vm.check_array(iov.base, iov.len as usize)?;
+                    vm.check_read_array(iov.base, iov.len as usize)?;
                 }
             }
         }
diff --git a/kernel/src/syscall/mem.rs b/kernel/src/syscall/mem.rs
index 6e04eab..f21a9cb 100644
--- a/kernel/src/syscall/mem.rs
+++ b/kernel/src/syscall/mem.rs
@@ -33,16 +33,16 @@ pub fn sys_mmap(
 
     if flags.contains(MmapFlags::FIXED) {
         // we have to map it to addr, so remove the old mapping first
-        proc.memory_set.pop_with_split(addr, addr + len);
+        proc.vm.pop_with_split(addr, addr + len);
     } else {
-        addr = proc.memory_set.find_free_area(addr, len);
+        addr = proc.vm.find_free_area(addr, len);
     }
 
     if flags.contains(MmapFlags::ANONYMOUS) {
         if flags.contains(MmapFlags::SHARED) {
             return Err(SysError::EINVAL);
         }
-        proc.memory_set.push(
+        proc.vm.push(
             addr,
             addr + len,
             prot.to_attr(),
@@ -66,11 +66,11 @@ pub fn sys_mprotect(addr: usize, len: usize, prot: usize) -> SysResult {
 
     // FIXME: properly set the attribute of the area
     //        now some mut ptr check is fault
-    let memory_area = proc.memory_set.iter().find(|area| area.contains(addr));
+    let memory_area = proc.vm.iter().find(|area| area.contains(addr));
     if memory_area.is_none() {
         return Err(SysError::ENOMEM);
     }
-    proc.memory_set.edit(|pt| {
+    proc.vm.edit(|pt| {
         for page in Page::range_of(addr, addr + len) {
             let entry = pt
                 .get_entry(page.start_address())
@@ -84,7 +84,7 @@ pub fn sys_mprotect(addr: usize, len: usize, prot: usize) -> SysResult {
 pub fn sys_munmap(addr: usize, len: usize) -> SysResult {
     info!("munmap addr={:#x}, size={:#x}", addr, len);
     let mut proc = process();
-    proc.memory_set.pop_with_split(addr, addr + len);
+    proc.vm.pop_with_split(addr, addr + len);
     Ok(0)
 }
 
diff --git a/kernel/src/syscall/misc.rs b/kernel/src/syscall/misc.rs
index e885320..d422e0f 100644
--- a/kernel/src/syscall/misc.rs
+++ b/kernel/src/syscall/misc.rs
@@ -22,8 +22,8 @@ pub fn sys_uname(buf: *mut u8) -> SysResult {
     let offset = 65;
     let strings = ["rCore", "orz", "0.1.0", "1", "machine", "domain"];
     let proc = process();
-    proc.memory_set
-        .check_mut_array(buf, strings.len() * offset)?;
+    proc.vm
+        .check_write_array(buf, strings.len() * offset)?;
 
     for i in 0..strings.len() {
         unsafe {
@@ -39,8 +39,8 @@ pub fn sys_sched_getaffinity(pid: usize, size: usize, mask: *mut u32) -> SysResu
         pid, size, mask
     );
     let proc = process();
-    proc.memory_set
-        .check_mut_array(mask, size / size_of::<u32>())?;
+    proc.vm
+        .check_write_array(mask, size / size_of::<u32>())?;
 
     // we only have 4 cpu at most.
     // so just set it.
@@ -52,7 +52,7 @@ pub fn sys_sched_getaffinity(pid: usize, size: usize, mask: *mut u32) -> SysResu
 
 pub fn sys_sysinfo(sys_info: *mut SysInfo) -> SysResult {
     let proc = process();
-    proc.memory_set.check_mut_ptr(sys_info)?;
+    proc.vm.check_write_ptr(sys_info)?;
 
     let sysinfo = SysInfo::default();
     unsafe { *sys_info = sysinfo };
@@ -76,13 +76,13 @@ pub fn sys_futex(uaddr: usize, op: u32, val: i32, timeout: *const TimeSpec) -> S
         return Err(SysError::EINVAL);
     }
     process()
-        .memory_set
-        .check_mut_ptr(uaddr as *mut AtomicI32)?;
+        .vm
+        .check_write_ptr(uaddr as *mut AtomicI32)?;
     let atomic = unsafe { &mut *(uaddr as *mut AtomicI32) };
     let timeout = if timeout.is_null() {
         None
     } else {
-        process().memory_set.check_ptr(timeout)?;
+        process().vm.check_read_ptr(timeout)?;
         Some(unsafe { *timeout })
     };
 
diff --git a/kernel/src/syscall/net.rs b/kernel/src/syscall/net.rs
index bb6f8d1..312411a 100644
--- a/kernel/src/syscall/net.rs
+++ b/kernel/src/syscall/net.rs
@@ -141,11 +141,11 @@ pub fn sys_getsockopt(
         fd, level, optname, optval, optlen
     );
     let proc = process();
-    proc.memory_set.check_mut_ptr(optlen)?;
+    proc.vm.check_write_ptr(optlen)?;
     match level {
         SOL_SOCKET => match optname {
             SO_SNDBUF => {
-                proc.memory_set.check_mut_array(optval, 4)?;
+                proc.vm.check_write_array(optval, 4)?;
                 unsafe {
                     *(optval as *mut u32) = TCP_SENDBUF as u32;
                     *optlen = 4;
@@ -153,7 +153,7 @@ pub fn sys_getsockopt(
                 Ok(0)
             }
             SO_RCVBUF => {
-                proc.memory_set.check_mut_array(optval, 4)?;
+                proc.vm.check_write_array(optval, 4)?;
                 unsafe {
                     *(optval as *mut u32) = TCP_RECVBUF as u32;
                     *optlen = 4;
@@ -269,7 +269,7 @@ pub fn sys_sendto(
     );
 
     let mut proc = process();
-    proc.memory_set.check_array(base, len)?;
+    proc.vm.check_read_array(base, len)?;
 
     let wrapper = proc.get_socket(fd)?;
     let endpoint = sockaddr_to_endpoint(&mut proc, addr, addr_len)?;
@@ -291,7 +291,7 @@ pub fn sys_recvfrom(
     );
 
     let mut proc = process();
-    proc.memory_set.check_mut_array(base, len)?;
+    proc.vm.check_write_array(base, len)?;
 
     let wrapper = proc.get_socket(fd)?;
     let mut slice = unsafe { slice::from_raw_parts_mut(base, len) };
@@ -674,7 +674,7 @@ fn sockaddr_to_endpoint(
     if len < size_of::<u16>() {
         return Err(SysError::EINVAL);
     }
-    proc.memory_set.check_array(addr as *const u8, len)?;
+    proc.vm.check_read_array(addr as *const u8, len)?;
     unsafe {
         match (*addr).family as usize {
             AF_INET => {
@@ -707,7 +707,7 @@ impl SockAddr {
             return Ok(0);
         }
 
-        proc.memory_set.check_mut_ptr(addr_len)?;
+        proc.vm.check_write_ptr(addr_len)?;
         let max_addr_len = *addr_len as usize;
         let full_len = match self.family as usize {
             AF_INET => size_of::<u16>() + size_of::<SockAddrIn>(),
@@ -717,8 +717,7 @@ impl SockAddr {
 
         let written_len = min(max_addr_len, full_len);
         if written_len > 0 {
-            proc.memory_set
-                .check_mut_array(addr as *mut u8, written_len)?;
+            proc.vm.check_write_array(addr as *mut u8, written_len)?;
             let source = slice::from_raw_parts(&self as *const SockAddr as *const u8, written_len);
             let target = slice::from_raw_parts_mut(addr as *mut u8, written_len);
             target.copy_from_slice(source);
diff --git a/kernel/src/syscall/proc.rs b/kernel/src/syscall/proc.rs
index 33aa8df..01cf63f 100644
--- a/kernel/src/syscall/proc.rs
+++ b/kernel/src/syscall/proc.rs
@@ -29,8 +29,8 @@ pub fn sys_clone(flags: usize, newsp: usize, parent_tid: *mut u32, child_tid: *m
     }
     {
         let proc = process();
-        proc.memory_set.check_mut_ptr(parent_tid)?;
-        proc.memory_set.check_mut_ptr(child_tid)?;
+        proc.vm.check_write_ptr(parent_tid)?;
+        proc.vm.check_write_ptr(child_tid)?;
     }
     let new_thread = current_thread().clone(tf, newsp, newtls, child_tid as usize);
     // FIXME: parent pid
@@ -48,7 +48,7 @@ pub fn sys_clone(flags: usize, newsp: usize, parent_tid: *mut u32, child_tid: *m
 pub fn sys_wait4(pid: isize, wstatus: *mut i32) -> SysResult {
     info!("wait4: pid: {}, code: {:?}", pid, wstatus);
     if !wstatus.is_null() {
-        process().memory_set.check_mut_ptr(wstatus)?;
+        process().vm.check_write_ptr(wstatus)?;
     }
     #[derive(Debug)]
     enum WaitFor {
@@ -56,7 +56,7 @@ pub fn sys_wait4(pid: isize, wstatus: *mut i32) -> SysResult {
         Pid(usize),
     }
     let target = match pid {
-        -1 => WaitFor::AnyChild,
+        -1 | 0 => WaitFor::AnyChild,
         p if p > 0 => WaitFor::Pid(p as usize),
         _ => unimplemented!(),
     };
@@ -99,7 +99,7 @@ pub fn sys_exec(name: *const u8, argv: *const *const u8, envp: *const *const u8,
     info!("exec: name: {:?}, argv: {:?} envp: {:?}", name, argv, envp);
     let proc = process();
     let name = if name.is_null() { String::from("") } else {
-        unsafe { proc.memory_set.check_and_clone_cstr(name)? }
+        unsafe { proc.vm.check_and_clone_cstr(name)? }
     };
 
     if argv.is_null() {
@@ -109,9 +109,9 @@ pub fn sys_exec(name: *const u8, argv: *const *const u8, envp: *const *const u8,
     let mut args = Vec::new();
     unsafe {
         let mut current_argv = argv as *const *const u8;
-        proc.memory_set.check_ptr(current_argv)?;
+        proc.vm.check_read_ptr(current_argv)?;
         while !(*current_argv).is_null() {
-            let arg = proc.memory_set.check_and_clone_cstr(*current_argv)?;
+            let arg = proc.vm.check_and_clone_cstr(*current_argv)?;
             args.push(arg);
             current_argv = current_argv.add(1);
         }
@@ -129,7 +129,7 @@ pub fn sys_exec(name: *const u8, argv: *const *const u8, envp: *const *const u8,
     thread.proc.lock().clone_for_exec(&proc);
 
     // Activate new page table
-    unsafe { thread.proc.lock().memory_set.activate(); }
+    unsafe { thread.proc.lock().vm.activate(); }
 
     // Modify the TrapFrame
     *tf = unsafe { thread.context.get_init_tf() };
@@ -259,7 +259,7 @@ pub fn sys_exit_group(exit_code: usize) -> ! {
 }
 
 pub fn sys_nanosleep(req: *const TimeSpec) -> SysResult {
-    process().memory_set.check_ptr(req)?;
+    process().vm.check_read_ptr(req)?;
     let time = unsafe { req.read() };
     info!("nanosleep: time: {:#?}", time);
     thread::sleep(time.to_duration());
diff --git a/kernel/src/syscall/time.rs b/kernel/src/syscall/time.rs
index c0be6d1..51d9666 100644
--- a/kernel/src/syscall/time.rs
+++ b/kernel/src/syscall/time.rs
@@ -78,7 +78,7 @@ pub fn sys_gettimeofday(tv: *mut TimeVal, tz: *const u8) -> SysResult {
     }
 
     let proc = process();
-    proc.memory_set.check_mut_ptr(tv)?;
+    proc.vm.check_write_ptr(tv)?;
 
     let timeval = TimeVal::get_epoch();
     unsafe {
@@ -91,7 +91,7 @@ pub fn sys_clock_gettime(clock: usize, ts: *mut TimeSpec) -> SysResult {
     info!("clock_gettime: clock: {:?}, ts: {:?}", clock, ts);
 
     let proc = process();
-    proc.memory_set.check_mut_ptr(ts)?;
+    proc.vm.check_write_ptr(ts)?;
 
     let timespec = TimeSpec::get_epoch();
     unsafe {
@@ -104,7 +104,7 @@ pub fn sys_time(time: *mut u64) -> SysResult {
     let sec = get_epoch_usec() / USEC_PER_SEC;
     if time as usize != 0 {
         let proc = process();
-        proc.memory_set.check_mut_ptr(time)?;
+        proc.vm.check_write_ptr(time)?;
         unsafe {
             time.write(sec as u64);
         }
@@ -122,7 +122,7 @@ pub struct RUsage {
 pub fn sys_getrusage(who: usize, rusage: *mut RUsage) -> SysResult {
     info!("getrusage: who: {}, rusage: {:?}", who, rusage);
     let proc = process();
-    proc.memory_set.check_mut_ptr(rusage)?;
+    proc.vm.check_write_ptr(rusage)?;
 
     let tick_base = *TICK_BASE;
     let tick = unsafe { crate::trap::TICK as u64 };