diff --git a/kernel/proc.c b/kernel/proc.c
index 130d9ce..5abb747 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -123,14 +123,20 @@ allocproc(void)
 
 found:
   p->pid = allocpid();
-  p->state = USED;
 
   // Allocate a trapframe page.
   if((p->trapframe = (struct trapframe *)kalloc()) == 0){
+    release(&p->lock);
+    return 0;
+  }
+
+  // Allocate a usyscall page.
+  if((p->usyscall = (struct usyscall *)kalloc()) == 0){
     freeproc(p);
     release(&p->lock);
     return 0;
   }
+  p->usyscall->pid =  p->pid ;
 
   // An empty user page table.
   p->pagetable = proc_pagetable(p);
@@ -155,6 +161,9 @@ found:
 static void
 freeproc(struct proc *p)
 {
+  if (p->usyscall) {
+    kfree((void*)p->usyscall);
+  }
   if(p->trapframe)
     kfree((void*)p->trapframe);
   p->trapframe = 0;
@@ -202,6 +211,16 @@ proc_pagetable(struct proc *p)
     return 0;
   }
 
+  // map the usyscall just below TRAMPOFRAME, for trampoline.S.
+  // 这个页需要设置PTE_U为，使得用户态可以访问
+  if(mappages(pagetable, USYSCALL, PGSIZE,
+              (uint64)(p->usyscall), PTE_R | PTE_U) < 0){
+    uvmunmap(pagetable, TRAPFRAME, 1, 0);
+    uvmunmap(pagetable, TRAMPOLINE, 1, 0);
+    uvmfree(pagetable, 0);
+    return 0;
+  }
+
   return pagetable;
 }
 
@@ -210,6 +229,7 @@ proc_pagetable(struct proc *p)
 void
 proc_freepagetable(pagetable_t pagetable, uint64 sz)
 {
+  uvmunmap(pagetable, USYSCALL, 1, 0);
   uvmunmap(pagetable, TRAMPOLINE, 1, 0);
   uvmunmap(pagetable, TRAPFRAME, 1, 0);
   uvmfree(pagetable, sz);
diff --git a/kernel/proc.h b/kernel/proc.h
index d021857..0af737d 100644
--- a/kernel/proc.h
+++ b/kernel/proc.h
@@ -94,11 +94,12 @@ struct proc {
 
   // wait_lock must be held when using this:
   struct proc *parent;         // Parent process
-
-  // these are private to the process, so p->lock need not be held.
+ // these are private to the process, so p->lock need not be held.
   uint64 kstack;               // Virtual address of kernel stack
   uint64 sz;                   // Size of process memory (bytes)
   pagetable_t pagetable;       // User page table
+  // 进程的结构体中需要加上usyscall字段
+  struct usyscall *usyscall;   // data page for usyscall
   struct trapframe *trapframe; // data page for trampoline.S
   struct context context;      // swtch() here to run process
   struct file *ofile[NOFILE];  // Open files
diff --git a/kernel/riscv.h b/kernel/riscv.h
index 6cfff1e..8bf202c 100644
--- a/kernel/riscv.h
+++ b/kernel/riscv.h
@@ -375,7 +375,9 @@ typedef uint64 *pagetable_t; // 512 PTEs
 #define PTE_W (1L << 2)
 #define PTE_X (1L << 3)
 #define PTE_U (1L << 4) // user can access
-
+#define PTE_A   (1L << 6) // Accessed bit
+#define PTE_D   (1L << 7) // Dirty bit
+#define PTE_PS  (1L << 7) // Page Size bit in PTE (for 2MB superpages)
 
 
 #if defined(LAB_MMAP) || defined(LAB_PGTBL)
diff --git a/kernel/syscall.c b/kernel/syscall.c
index 4aea542..968fbc7 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -111,6 +111,7 @@ extern uint64 sys_recv(void);
 #ifdef LAB_PGTBL
 extern uint64 sys_pgpte(void);
 extern uint64 sys_kpgtbl(void);
+extern uint64 sys_pgaccess(void);
 #endif
 
 // An array mapping syscall numbers from syscall.h
@@ -146,6 +147,7 @@ static uint64 (*syscalls[])(void) = {
 #ifdef LAB_PGTBL
 [SYS_pgpte] sys_pgpte,
 [SYS_kpgtbl] sys_kpgtbl,
+[SYS_pgaccess] sys_pgaccess,
 #endif
 };
 
diff --git a/kernel/sysproc.c b/kernel/sysproc.c
index d9b7f9c..2e3b7be 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -123,3 +123,41 @@ sys_uptime(void)
   release(&tickslock);
   return xticks;
 }
+
+uint64
+sys_pgaccess(void)
+{
+  uint64 va;
+  int n;
+  uint64 user_mask_addr;
+  argaddr(0, &va);
+  argint(1, &n);
+  argaddr(2, &user_mask_addr);
+  if (va < 0 || n < 0 || user_mask_addr < 0)
+    return -1;
+
+  if (n < 0 || n > 32)
+    return -1;
+
+  struct proc *p = myproc();
+  uint64 mask = 0;
+
+  for (int i = 0; i < n; i++) {
+    uint64 v = va + i * PGSIZE;
+    pte_t *pte = walk(p->pagetable, v, 0);
+
+    if (!pte || (*pte & PTE_PS))
+      continue;
+
+    if ((*pte & PTE_V) && (*pte & PTE_A)) {
+      mask |= (1 << i);       // Set bit i in mask
+      *pte &= ~PTE_A;         // Clear the Accessed bit
+    }
+  }
+
+  if (copyout(p->pagetable, user_mask_addr, (char*)&mask, sizeof(mask)) < 0)
+    return -1;
+
+  return 0;
+}
+
diff --git a/kernel/vm.c b/kernel/vm.c
index 7f388fe..1e9a6d8 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -101,6 +101,9 @@ walk(pagetable_t pagetable, uint64 va, int alloc)
   for(int level = 2; level > 0; level--) {
     pte_t *pte = &pagetable[PX(level, va)];
     if(*pte & PTE_V) {
+      if (*pte & PTE_PS) { // 如果是 Superpage
+        return pte;
+      }
       pagetable = (pagetable_t)PTE2PA(*pte);
 #ifdef LAB_PGTBL
       if(PTE_LEAF(*pte)) {