ARM: 8292/1: mm: fix size rounding-down of arm_add_memory() function

The current rounding of "size" is wrong:

 - If "start" is sufficiently near the next page boundary, "size"
   is decremented by more than enough and the last page is lost.

 - If "size" is sufficiently small, it is wrapped around and gets
   a bogus value.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/setup.c

@@ -657,10 +657,13 @@ int __init arm_add_memory(u64 start, u64 size)
 
 	/*
 	 * Ensure that start/size are aligned to a page boundary.
-	 * Size is appropriately rounded down, start is rounded up.
+	 * Size is rounded down, start is rounded up.
 	 */
-	size -= start & ~PAGE_MASK;
 	aligned_start = PAGE_ALIGN(start);
+	if (aligned_start > start + size)
+		size = 0;
+	else
+		size -= aligned_start - start;
 
 #ifndef CONFIG_ARCH_PHYS_ADDR_T_64BIT
 	if (aligned_start > ULONG_MAX) {