+/* 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. */
+#define PF_U 0x4 /* 0: kernel, 1: user process. */
+
+/* Page fault handler. This is a skeleton that must be filled in
+ to implement virtual memory. Some solutions to project 2 may
+ also require modifying this code.
+
+ At entry, the address that faulted is in CR2 (Control Register
+ 2) and information about the fault, formatted as described in
+ the PF_* macros above, is in F's error_code member. The
+ example code here shows how to parse that information. You
+ can find more information about both of these in the
+ description of "Interrupt 14--Page Fault Exception (#PF)" in
+ [IA32-v3] section 5.14, which is pages 5-46 to 5-49. */
+static void
+page_fault (struct intr_frame *f)
+{
+ bool not_present; /* True: not-present page, false: writing r/o page. */
+ bool write; /* True: access was write, false: access was read. */
+ bool user; /* True: access by user, false: access by kernel. */
+ void *fault_addr; /* Fault address. */
+
+ /* Obtain faulting address, the virtual address that was
+ accessed to cause the fault. It may point to code or to
+ data. It is not necessarily the address of the instruction
+ that caused the fault (that's f->eip). */
+ asm ("movl %%cr2, %0" : "=r" (fault_addr));
+
+ /* Turn interrupts back on (they were only off so that we could
+ be assured of reading CR2 before it changed). */
+ intr_enable ();
+
+ /* Determine cause. */
+ not_present = (f->error_code & PF_P) == 0;
+ write = (f->error_code & PF_W) != 0;
+ user = (f->error_code & PF_U) != 0;
+
+ /* To implement virtual memory, delete the rest of the function
+ body, and replace it with code that brings in the page to
+ which fault_addr refers. */
+ printf ("Page fault at %p: %s error %s page in %s context.\n",
+ fault_addr,
+ not_present ? "not present" : "rights violation",
+ write ? "writing" : "reading",
+ user ? "user" : "kernel");
+ kill (f);
+}
+