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>

1 files changed, 5 insertions, 2 deletions

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index f9c863911038..d13f185e7bd5 100644
--- a/arch/arm/kernel/setup.c
+++ b/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) {