+/*
+ * Check that @page is mapped at @address into @mm.
+ *
+ * On success returns with mapped pte and locked mm->page_table_lock.
+ */
+static pte_t *page_check_address(struct page *page, struct mm_struct *mm,
+ unsigned long address)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *pte;
+
+ /*
+ * We need the page_table_lock to protect us from page faults,
+ * munmap, fork, etc...
+ */
+ spin_lock(&mm->page_table_lock);
+ pgd = pgd_offset(mm, address);
+ if (likely(pgd_present(*pgd))) {
+ pud = pud_offset(pgd, address);
+ if (likely(pud_present(*pud))) {
+ pmd = pmd_offset(pud, address);
+ if (likely(pmd_present(*pmd))) {
+ pte = pte_offset_map(pmd, address);
+ if (likely(pte_present(*pte) &&
+ page_to_pfn(page) == pte_pfn(*pte)))
+ return pte;
+ pte_unmap(pte);
+ }
+ }
+ }
+ spin_unlock(&mm->page_table_lock);
+ return ERR_PTR(-ENOENT);
+}
+