[PATCH] fix x86 page table init

[Brian Gerst <bgerst@quark.didntduck.org>]

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The recent changes to the x86 page table init reintroduced a bug with 
the 4k pagetables.  The page table must be filled with entries before it 
is inserted into the pmd or else you risk a tlb miss on a kernel code 
page causing an oops.  This patch takes a different approach than before 
- it allows for reuse of the boot pagetable pages instead of allocating 
new ones.

--
				Brian Gerst

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diff -urN linux-bk/arch/i386/mm/init.c linux/arch/i386/mm/init.c
--- linux-bk/arch/i386/mm/init.c	Tue Jul 30 20:59:27 2002
+++ linux/arch/i386/mm/init.c	Tue Jul 30 21:02:41 2002
@@ -70,10 +70,14 @@
  */
 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) | _KERNPG_TABLE));
-	if (page_table != pte_offset_kernel(pmd, 0))
-		BUG();	
+	pte_t *page_table;
+	page_table = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
+	if (pmd_none(*pmd)) {
+		set_pmd(pmd, __pmd(__pa(page_table) | _KERNPG_TABLE));
+		if (page_table != pte_offset_kernel(pmd, 0))
+			BUG();	
+	} else
+		page_table = pte_offset_kernel(pmd, 0);
 
 	return page_table;
 }
@@ -107,9 +111,7 @@
 
 		pmd = pmd_offset(pgd, vaddr);
 		for (; (pmd_ofs < PTRS_PER_PMD) && (vaddr != end); pmd++, pmd_ofs++) {
-			if (pmd_none(*pmd)) 
-				one_page_table_init(pmd);
-
+			one_page_table_init(pmd);
 			vaddr += PMD_SIZE;
 		}
 		pmd_ofs = 0;