feat: implement page swapping

src/userprog/exception.c

@@ -1,10 +1,18 @@
 #include "userprog/exception.h"
 #include <inttypes.h>
 #include <stdio.h>
+#include "stdbool.h"
 #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"
+#endif
 
 /* Number of page faults processed. */
 static long long page_fault_cnt;
@@ -147,10 +155,27 @@ page_fault (struct intr_frame *f)
   user = (f->error_code & PF_U) != 0;
 
 #ifdef VM
-  if (user && not_present)
+  if (user)
     {
+      if (not_present)
+        {
+          struct thread *t = thread_current ();
+          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);
+
+              bool writeable = pagedir_is_writable (t->pagedir, upage);
+              if (pagedir_set_page (t->pagedir, upage, kpage, writeable)) return;
+            }
+
+          /* Handle page faults that need to be resolved by dynamic stack growth
+             by checking if this is such a fault and resolving it appropriately. */
           if (handle_stack_fault (fault_addr, f->esp)) return;
         }
+    }
   else
     {
       f->eip = (void *)f->eax;

src/vm/page.c

@@ -24,6 +24,16 @@ page_set_swap (struct thread *owner, void *upage, size_t swap_slot)
    pagedir_clear_page (owner->pagedir, upage);
 }
 
+/* Returns true iff the page with user address 'upage' owned by 'owner' 
+   is flagged to be in the swap disk via the owner's page table. */
+bool
+page_in_swap (struct thread *owner, void *upage)
+{
+   uint32_t *pte = lookup_page (owner->pagedir, upage, false);
+   return pte != NULL &&
+          (*pte & (1 << SWAP_FLAG_BIT)) != 0;
+}
+
 /* Given that the page with user address 'upage' owned by 'owner' is flagged
    to be in the swap disk via the owner's page table, returns its stored
    swap slot. Otherwise panics the kernel. */
@@ -32,8 +42,8 @@ page_get_swap (struct thread *owner, void *upage)
 {
    uint32_t *pte = lookup_page (owner->pagedir, upage, false);
 
+   ASSERT (pte != NULL);
    ASSERT ((*pte & PTE_P) == 0);
-   ASSERT ((*pte & (1 << SWAP_FLAG_BIT)) != 0);
 
    /* Masks the address bits and returns truncated value. */
    return ((*pte & PTE_ADDR) >> ADDR_START_BIT);

src/vm/page.h

@@ -4,6 +4,7 @@
 #include "threads/thread.h"
 
 void page_set_swap (struct thread *, void *, size_t);
+bool page_in_swap (struct thread *, void *);
 size_t page_get_swap (struct thread *, void *);
 
 #endif /* vm/frame.h */