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refactor: add comments describing each type of page fault dealt by the page fault handler

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Themis Demetriades
2024-12-03 21:47:59 +00:00
parent 9a3c8a1c38
commit 47a7dfae04
1 changed files with 12 additions and 5 deletions
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17
src/userprog/exception.c
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@@ -155,11 +155,15 @@ page_fault (struct intr_frame *f)
user = (f->error_code & PF_U) != 0; user = (f->error_code & PF_U) != 0;
#ifdef VM #ifdef VM
struct thread *t = thread_current ();
if (user) if (user)
{ {
if (not_present) if (not_present)
{ {
struct thread *t = thread_current (); /* Check if the non-present user page is in the swap partition.
If so, swap it back into main memory, updating the PTE for
the faulted virtual address to point to the newly allocated
frame. */
if (page_in_swap (t, fault_addr)) if (page_in_swap (t, fault_addr))
{ {
size_t swap_slot = page_get_swap (t, fault_addr); size_t swap_slot = page_get_swap (t, fault_addr);
@@ -171,15 +175,18 @@ page_fault (struct intr_frame *f)
if (pagedir_set_page (t->pagedir, upage, kpage, writeable)) return; if (pagedir_set_page (t->pagedir, upage, kpage, writeable)) return;
} }
/* Handle page faults that need to be resolved by dynamic stack growth /* Handle user page faults that need to be resolved by dynamic
by checking if this is such a fault and resolving it appropriately. */ stack growth by checking if this is such a fault and responding
accordingly. */
if (handle_stack_fault (fault_addr, f->esp)) return; if (handle_stack_fault (fault_addr, f->esp)) return;
} }
} }
else else
{ {
/* Allows for stack growth in kernel context, due to syscall failure */ /* Handle kernel page faults that need to be resolved by dynamic stack
if (handle_stack_fault (fault_addr, thread_current ()->curr_esp)) return; growth by checking if this is such a fault and responding
accordingly. */
if (not_present && handle_stack_fault (fault_addr, t->curr_esp)) return;
f->eip = (void *)f->eax; f->eip = (void *)f->eax;
f->eax = 0xffffffff; f->eax = 0xffffffff;