/*
* 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;
}
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))));
}