Пример #1
0
/*
 * This routine handles present pages, when users try to write
 * to a shared page. It is done by copying the page to a new address
 * and decrementing the shared-page counter for the old page.
 *
 * Goto-purists beware: the only reason for goto's here is that it results
 * in better assembly code.. The "default" path will see no jumps at all.
 *
 * Note that this routine assumes that the protection checks have been
 * done by the caller (the low-level page fault routine in most cases).
 * Thus we can safely just mark it writable once we've done any necessary
 * COW.
 *
 * We also mark the page dirty at this point even though the page will
 * change only once the write actually happens. This avoids a few races,
 * and potentially makes it more efficient.
 *
 * We hold the mm semaphore and the page_table_lock on entry and exit
 * with the page_table_lock released.
 */
static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma,
	unsigned long address, pte_t *page_table, pte_t pte)
{
	struct page *old_page, *new_page;

	old_page = pte_page(pte);
	if (!VALID_PAGE(old_page))
		goto bad_wp_page;

	if (!TryLockPage(old_page)) {
		int reuse = can_share_swap_page(old_page);
		unlock_page(old_page);
		if (reuse) {
#ifndef CONFIG_SUPERH
			/* Not needed for VIPT cache */
			flush_cache_page(vma, address);
#endif
			establish_pte(vma, address, page_table, pte_mkyoung(pte_mkdirty(pte_mkwrite(pte))));
			spin_unlock(&mm->page_table_lock);
			return 1;	/* Minor fault */
		}
	}

	/*
	 * Ok, we need to copy. Oh, well..
	 */
	page_cache_get(old_page);
	spin_unlock(&mm->page_table_lock);

	new_page = alloc_page(GFP_HIGHUSER);
	if (!new_page)
		goto no_mem;
	copy_cow_page(old_page,new_page,address);

	/*
	 * Re-check the pte - we dropped the lock
	 */
	spin_lock(&mm->page_table_lock);
	if (pte_same(*page_table, pte)) {
		if (PageReserved(old_page))
			++mm->rss;
		break_cow(vma, new_page, address, page_table);
		lru_cache_add(new_page);

		/* Free the old page.. */
		new_page = old_page;
	}
	spin_unlock(&mm->page_table_lock);
	page_cache_release(new_page);
	page_cache_release(old_page);
	return 1;	/* Minor fault */

bad_wp_page:
	spin_unlock(&mm->page_table_lock);
	printk("do_wp_page: bogus page at address %08lx (page 0x%lx)\n",address,(unsigned long)old_page);
	return -1;
no_mem:
	page_cache_release(old_page);
	return -1;
}
Пример #2
0
/*
 * We hold the mm semaphore and the page_table_lock on entry and
 * should release the pagetable lock on exit..
 */
static int do_swap_page(struct mm_struct * mm,
	struct vm_area_struct * vma, unsigned long address,
	pte_t * page_table, pte_t orig_pte, int write_access)
{
	struct page *page;
	swp_entry_t entry = pte_to_swp_entry(orig_pte);
	pte_t pte;
	int ret = 1;

	spin_unlock(&mm->page_table_lock);
	page = lookup_swap_cache(entry);
	if (!page) {
		swapin_readahead(entry);
		page = read_swap_cache_async(entry);
		if (!page) {
			/*
			 * Back out if somebody else faulted in this pte while
			 * we released the page table lock.
			 */
			int retval;
			spin_lock(&mm->page_table_lock);
			retval = pte_same(*page_table, orig_pte) ? -1 : 1;
			spin_unlock(&mm->page_table_lock);
			return retval;
		}

		/* Had to read the page from swap area: Major fault */
		ret = 2;
	}

	lock_page(page);

	/*
	 * Back out if somebody else faulted in this pte while we
	 * released the page table lock.
	 */
	spin_lock(&mm->page_table_lock);
	if (!pte_same(*page_table, orig_pte)) {
		spin_unlock(&mm->page_table_lock);
		unlock_page(page);
		page_cache_release(page);
		return 1;
	}

	/* The page isn't present yet, go ahead with the fault. */
		
	swap_free(entry);
	if (vm_swap_full())
		remove_exclusive_swap_page(page);

	mm->rss++;
	pte = mk_pte(page, vma->vm_page_prot);
	if (write_access && can_share_swap_page(page))
		pte = pte_mkdirty(pte_mkwrite(pte));
	unlock_page(page);

	flush_page_to_ram(page);
	flush_icache_page(vma, page);
	set_pte(page_table, pte);

	/* No need to invalidate - it was non-present before */
	update_mmu_cache(vma, address, pte);
	spin_unlock(&mm->page_table_lock);
	return ret;
}