[PATCH] ARM: mm: enforce pageblock alignment when freeing memmap entries at init

[dima@android.com (Dima Zavin)]

On some machines, the nodes do not always start on pageblock
boundaries. In these cases it is possible for free_unused_memmap
to free mappings for pages inside a pageblock with otherwise
valid pages. This presents problems for page migration since it
operates on whole pageblocks at a time.

Round down bank_start to pageblock boundary so that whole
pageblocks always have valid mappings.

Signed-off-by: Dima Zavin <dima@android.com>
---
 arch/arm/mm/init.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 5164069..98de5d8 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -418,7 +418,11 @@ static void __init free_unused_memmap(struct meminfo *mi)
 	for_each_bank(i, mi) {
 		struct membank *bank = &mi->bank[i];
 
-		bank_start = bank_pfn_start(bank);
+		/* Round bank_start down to the start of a pageblock so that
+		 * all pages in a pageblock always have a mapping.
+		 */
+		bank_start = round_down(bank_pfn_start(bank),
+					MAX_ORDER_NR_PAGES);
 
 		/*
 		 * If we had a previous bank, and there is a space
-- 
1.7.3.1