示例#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;
}
示例#2
0
文件: memory.c 项目: davidbau/davej
static inline void break_cow(struct vm_area_struct * vma, struct page *	old_page, struct page * new_page, unsigned long address, 
		pte_t *page_table)
{
	copy_cow_page(old_page,new_page,address);
	flush_page_to_ram(new_page);
	flush_cache_page(vma, address);
	establish_pte(vma, address, page_table, pte_mkwrite(pte_mkdirty(mk_pte(new_page, vma->vm_page_prot))));
}