[PATCH] x86 page table initialization fix

At bootup, one_page_table_init() pulls the rug out from under the kernel
by installing a new page table before setting it up.  With big TLB's, it
can go unnoticed, but a 486 has a small TLB so any miss will cause a
triple fault and reset.

arch/i386/mm/init.c

@@ -71,12 +71,16 @@ static pmd_t * __init one_md_table_init(pgd_t *pgd)
  */
 static pte_t * __init one_page_table_init(pmd_t *pmd)
 {
-	pte_t *page_table = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
-	set_pmd(pmd, __pmd(__pa(page_table) | _PAGE_TABLE));
-	if (page_table != pte_offset_kernel(pmd, 0))
-		BUG();	
+	if (pmd_none(*pmd)) {
+		pte_t *page_table = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
+		set_pmd(pmd, __pmd(__pa(page_table) | _PAGE_TABLE));
+		if (page_table != pte_offset_kernel(pmd, 0))
+			BUG();	
 
-	return page_table;
+		return page_table;
+	}
+	
+	return pte_offset_kernel(pmd, 0);
 }
 
 /*