x86: fix trim mtrr not to setup_memory two times

we could call find_max_pfn() directly instead of setup_memory() to get
max_pfn needed for mtrr trimming.

otherwise setup_memory() is called two times... that is duplicated...

[ mingo@elte.hu: both Thomas and me simulated a double call to
  setup_bootmem_allocator() and can confirm that it is a real bug
  which can hang in certain configs. It's not been reported yet but
  that is probably due to the relatively scarce nature of
  MTRR-trimming systems. ]

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/setup_32.c

@@ -406,8 +406,6 @@ static unsigned long __init setup_memory(void)
 	 */
 	min_low_pfn = PFN_UP(init_pg_tables_end);
 
-	find_max_pfn();
-
 	max_low_pfn = find_max_low_pfn();
 
 #ifdef CONFIG_HIGHMEM
@@ -764,12 +762,13 @@ void __init setup_arch(char **cmdline_p)
 	if (efi_enabled)
 		efi_init();
 
-	max_low_pfn = setup_memory();
-
 	/* update e820 for memory not covered by WB MTRRs */
+	find_max_pfn();
 	mtrr_bp_init();
 	if (mtrr_trim_uncached_memory(max_pfn))
-		max_low_pfn = setup_memory();
+		find_max_pfn();
+
+	max_low_pfn = setup_memory();
 
 #ifdef CONFIG_VMI
 	/*

arch/x86/mm/discontig_32.c

@@ -324,7 +324,6 @@ unsigned long __init setup_memory(void)
 	 * this space and use it to adjust the boundary between ZONE_NORMAL
 	 * and ZONE_HIGHMEM.
 	 */
-	find_max_pfn();
 	get_memcfg_numa();
 
 	kva_pages = calculate_numa_remap_pages();