x86: enable memory tester support on 32-bit

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

Documentation/kernel-parameters.txt

@@ -1206,7 +1206,7 @@ and is between 256 and 4096 characters. It is defined in the file
 			         or
 			         memmap=0x10000$0x18690000
 
-	memtest=	[KNL,X86_64] Enable memtest
+	memtest=	[KNL,X86] Enable memtest
 			Format: <integer>
 			range: 0,4 : pattern number
 			default : 0 <disable>

arch/x86/Kconfig

@@ -447,7 +447,6 @@ config PARAVIRT_DEBUG
 
 config MEMTEST
 	bool "Memtest"
-	depends on X86_64
 	help
 	  This option adds a kernel parameter 'memtest', which allows memtest
 	  to be set.

arch/x86/mm/init_32.c

@@ -844,6 +844,9 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
 		reserve_early(table_start << PAGE_SHIFT,
 				 table_end << PAGE_SHIFT, "PGTABLE");
 
+	if (!after_init_bootmem)
+		early_memtest(start, end);
+
 	return end >> PAGE_SHIFT;
 }