x86: extend e820 early_res support 32bit -fix #3

introduce init_pg_table_start, so xen PV could specify the value.

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c8a56e4..ccc7b84 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1211,6 +1211,7 @@
 
 	pgd = (pgd_t *)xen_start_info->pt_base;
 
+	init_pg_tables_start = __pa(pgd);
 	init_pg_tables_end = __pa(pgd) + xen_start_info->nr_pt_frames*PAGE_SIZE;
 
 	init_mm.pgd = pgd; /* use the Xen pagetables to start */
@@ -1246,5 +1247,5 @@
 		add_preferred_console("hvc", 0, NULL);
 
 	/* Start the world */
-	start_kernel();
+	i386_start_kernel();
 }