fix: invalidate PTEs of evicted pages before eviction occurs to prevent modificationof pages mid-eviction

src/userprog/pagedir.c

@@ -7,7 +7,6 @@
 #include "threads/palloc.h"
 
 static uint32_t *active_pd (void);
-static void invalidate_pagedir (uint32_t *);
 
 /* Creates a new page directory that has mappings for kernel
    virtual addresses, but none for user virtual addresses.
@@ -278,7 +277,7 @@ active_pd (void)
    This function invalidates the TLB if PD is the active page
    directory.  (If PD is not active then its entries are not in
    the TLB, so there is no need to invalidate anything.) */
-static void
+void
 invalidate_pagedir (uint32_t *pd) 
 {
   if (active_pd () == pd) 

src/userprog/pagedir.h

@@ -17,5 +17,6 @@ void pagedir_set_accessed (uint32_t *pd, const void *upage, bool accessed);
 bool pagedir_is_writable (uint32_t *pd, const void *upage);
 void pagedir_set_writable (uint32_t *pd, const void *upage, bool writable);
 void pagedir_activate (uint32_t *pd);
+void invalidate_pagedir (uint32_t *pd);
 
 #endif /* userprog/pagedir.h */