Imperial-MEng/pintos_22
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fix: invalidate PTEs of evicted pages before eviction occurs to prevent modificationof pages mid-eviction

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Themis Demetriades
2024-12-04 15:02:49 +00:00
parent 47a7dfae04
commit 1b73e415d7
4 changed files with 12 additions and 7 deletions
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7
src/vm/frame.c
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@@ -93,6 +93,13 @@ frame_alloc (enum palloc_flags flags, void *upage, struct thread *owner)
ASSERT (victim != NULL); /* get_victim () should never return null. */
/* 2. Swap out victim into disk. */
/* Mark page as 'not present' and flag the page directory as having
been modified *before* eviction begins to prevent the owner of the
victim page from accessing/modifying it mid-eviction. */
pagedir_clear_page (owner->pagedir, upage);
// TODO: Lock PTE of victim page for victim process.
size_t swap_slot = swap_out (victim->frame);
page_set_swap (victim->owner, victim->upage, swap_slot);

8
src/vm/page.c
View File

@@ -6,8 +6,8 @@
#define ADDR_START_BIT 12
/* Updates the 'owner' thread's page table entry for virtual address 'upage'
to have a present bit of 0 and stores the specified swap slot value in the
entry for later retrieval from disk. */
to flag the page as being stored in swap, and stores the specified swap slot
value in the entry at the address bits for later retrieval from disk. */
void
page_set_swap (struct thread *owner, void *upage, size_t swap_slot)
{
@@ -19,9 +19,7 @@ page_set_swap (struct thread *owner, void *upage, size_t swap_slot)
uint32_t swap_slot_bits = (swap_slot << ADDR_START_BIT) & PTE_ADDR;
*pte = (*pte & PTE_FLAGS) | swap_slot_bits;
/* Mark page as 'not present' and flag the page directory as having
been modified. */
pagedir_clear_page (owner->pagedir, upage);
invalidate_pagedir (owner->pagedir);
}
/* Returns true iff the page with user address 'upage' owned by 'owner'