src/threads/thread.c

@@ -15,6 +15,7 @@
 #include "threads/switch.h"
 #include "threads/synch.h"
 #include "threads/vaddr.h"
+#include "vm/page.h"
 #ifdef USERPROG
 #include "userprog/process.h"
 #include "userprog/syscall.h"
@@ -264,7 +265,8 @@ thread_create (const char *name, int priority,
 
   if (!hash_init (&t->open_files, fd_hash, fd_less, NULL)
       || !hash_init (&t->child_results, process_result_hash,
-                     process_result_less, t))
+                     process_result_less, t)
+      || !hash_init (&t->pages, page_hash, page_less, NULL))
     {
       palloc_free_page (t);
       free (t->result);

src/userprog/exception.c

@@ -5,13 +5,13 @@
 #include "userprog/gdt.h"
 #include "threads/interrupt.h"
 #include "threads/thread.h"
-#include "userprog/pagedir.h"
 #ifdef VM
 #include "vm/stackgrowth.h"
 #include "vm/frame.h"
 #include "vm/page.h"
 #include "devices/swap.h"
 #include "threads/vaddr.h"
+#include "userprog/pagedir.h"
 #endif
 
 /* Number of page faults processed. */
@@ -19,6 +19,7 @@ static long long page_fault_cnt;
 
 static void kill (struct intr_frame *);
 static void page_fault (struct intr_frame *);
+bool try_fetch_page (void *upage, bool write);
 
 /* Registers handlers for interrupts that can be caused by user
    programs.
@@ -156,6 +157,7 @@ page_fault (struct intr_frame *f)
 
 #ifdef VM
   struct thread *t = thread_current ();
+  void *upage = pg_round_down (fault_addr);
   if (user)
     {
       if (not_present)
@@ -167,7 +169,6 @@ page_fault (struct intr_frame *f)
           if (page_in_swap (t, fault_addr))
             {
               size_t swap_slot = page_get_swap (t, fault_addr);
-              void *upage = pg_round_down (fault_addr);
               void *kpage = frame_alloc (0, upage, t);
               swap_in (kpage, swap_slot);
 
@@ -192,6 +193,15 @@ page_fault (struct intr_frame *f)
       f->eax = 0xffffffff;
       return;
     }
+
+  /* If the fault address is in a user page that is not present, then it might
+  just need to be lazily loaded. So, we check our SPT to see if the page
+  is expected to have data loaded in memory. */
+  if (not_present && is_user_vaddr (upage) && upage != NULL)
+    {
+      if (try_fetch_page (upage, write))
+        return;
+    }
 #endif
 
   /* To implement virtual memory, delete the rest of the function
@@ -205,3 +215,32 @@ page_fault (struct intr_frame *f)
   kill (f);
 }
 
+bool
+try_fetch_page (void *upage, bool write)
+{
+  /* Check if the page is in the supplemental page table. That is, it is a page
+     that is expected to be in memory. */
+  struct page_entry *page = page_get (upage);
+  if (page == NULL)
+    return false;
+
+  /* An attempt to write to a non-writeable should fail. */
+  if (write && !page->writable)
+    return false;
+
+  /* Load the page into memory based on the type of data it is expecting. */
+  bool success = false;
+  switch (page->type) {
+    case PAGE_EXECUTABLE:
+      success = page_load (page, page->writable);
+      break;
+    default:
+      return false;
+  }
+
+  if (success && page->writable &&
+      !pagedir_is_writable(thread_current()->pagedir, upage))
+    pagedir_set_writable(thread_current()->pagedir, upage, true);
+
+  return success;
+}

src/userprog/exception.h

@@ -1,6 +1,8 @@
 #ifndef USERPROG_EXCEPTION_H
 #define USERPROG_EXCEPTION_H
 
+#include <stdbool.h>
+
 /* Page fault error code bits that describe the cause of the exception.  */
 #define PF_P 0x1    /* 0: not-present page. 1: access rights violation. */
 #define PF_W 0x2    /* 0: read, 1: write. */
@@ -8,5 +10,7 @@
 
 void exception_init (void);
 void exception_print_stats (void);
+bool
+try_fetch_page (void *upage, bool write);
 
 #endif /* userprog/exception.h */

src/userprog/process.c

@@ -24,6 +24,7 @@
 #include "threads/vaddr.h"
 #include "threads/synch.h"
 #include "devices/timer.h"
+#include "vm/page.h"
 #ifdef VM
 #include "vm/frame.h"
 #endif
@@ -118,6 +119,7 @@ process_execute (const char *cmd)
 
 static void *get_usr_kpage (enum palloc_flags flags, void *upage);
 static void free_usr_kpage (void *kpage);
+bool install_page (void *upage, void *kpage, bool writable);
 
 static bool process_init_stack (char *cmd_saveptr, void **esp, char *file_name);
 static void *push_to_stack (void **esp, void *data, size_t data_size);
@@ -363,6 +365,7 @@ process_exit (void)
 
   /* Clean up all open files */
   hash_destroy (&cur->open_files, fd_cleanup);
+  hash_destroy (&cur->pages, page_cleanup);
 
   /* Close the executable file, implicitly allowing it to be written to. */
   if (cur->exec_file != NULL)
@@ -620,7 +623,6 @@ load (const char *file_name, void (**eip) (void), void **esp)
 
  done:
   /* We arrive here whether the load is successful or not. */
-  file_close (file);
   lock_release (&filesys_lock);
   return success;
 }
@@ -688,58 +690,29 @@ validate_segment (const struct Elf32_Phdr *phdr, struct file *file)
    or disk read error occurs. */
 static bool
 load_segment (struct file *file, off_t ofs, uint8_t *upage,
-              uint32_t read_bytes, uint32_t zero_bytes, bool writable) 
+              uint32_t read_bytes, uint32_t zero_bytes, bool writable)
 {
   ASSERT ((read_bytes + zero_bytes) % PGSIZE == 0);
   ASSERT (pg_ofs (upage) == 0);
   ASSERT (ofs % PGSIZE == 0);
 
-  file_seek (file, ofs);
-  while (read_bytes > 0 || zero_bytes > 0) 
+  while (read_bytes > 0 || zero_bytes > 0)
     {
       /* Calculate how to fill this page.
          We will read PAGE_READ_BYTES bytes from FILE
          and zero the final PAGE_ZERO_BYTES bytes. */
       size_t page_read_bytes = read_bytes < PGSIZE ? read_bytes : PGSIZE;
       size_t page_zero_bytes = PGSIZE - page_read_bytes;
-      
-      /* Check if virtual page already allocated */
-      struct thread *t = thread_current ();
-      uint8_t *kpage = pagedir_get_page (t->pagedir, upage);
-      
-      if (kpage == NULL){
-        
-        /* Get a new page of memory. */
-        kpage = get_usr_kpage (0, upage);
-        if (kpage == NULL){
-          return false;
-        }
-        
-        /* Add the page to the process's address space. */
-        if (!install_page (upage, kpage, writable)) 
-        {
-          free_usr_kpage (kpage);
-          return false; 
-        }     
-        
-      } else {
-        
-        /* Check if writable flag for the page should be updated */
-        if(writable && !pagedir_is_writable(t->pagedir, upage)){
-          pagedir_set_writable(t->pagedir, upage, writable); 
-        }
-        
-      }
 
-      /* Load data into the page. */
-      if (file_read (file, kpage, page_read_bytes) != (int) page_read_bytes){
-        return false; 
-      }
-      memset (kpage + page_read_bytes, 0, page_zero_bytes);
+      /* Add the page metadata to the SPT to be lazy loaded later on */
+      if (page_insert (file, ofs, upage, page_read_bytes, page_zero_bytes,
+                       writable, PAGE_EXECUTABLE) == NULL)
+        return false;
 
       /* Advance. */
       read_bytes -= page_read_bytes;
       zero_bytes -= page_zero_bytes;
+      ofs += PGSIZE;
       upage += PGSIZE;
     }
   return true;

src/userprog/syscall.c

@@ -536,4 +536,4 @@ put_user (uint8_t *udst, uint8_t byte)
        : "=&a"(error_code), "=m"(*udst)
        : "q"(byte));
   return error_code != -1;
-}
+}

src/vm/frame.c

@@ -260,4 +260,3 @@ lru_prev (struct list_elem *e)
 
   return list_prev (e);
 }
-

src/vm/page.c

@@ -154,4 +154,3 @@ page_get_swap (struct thread *owner, void *upage)
    /* Masks the address bits and returns truncated value. */
    return ((*pte & PTE_ADDR) >> ADDR_START_BIT);
 }
-