[PATCH v1 2/4] mm/memory_hotplug: Handle unaligned start and nr_pages in online_pages_blocks()

[David Hildenbrand]

Take care of nr_pages not being a power of two and start not being
properly aligned. Essentially, what walk_system_ram_range() could provide
to us. get_order() will round-up in case it's not a power of two.

This should only apply to memory blocks that contain strange memory
resources (especially with holes), not to ordinary DIMMs.

Fixes: a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher order")
Cc: Arun KS <arunks@xxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 mm/memory_hotplug.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 3706a137d880..2abd938c8c45 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -640,6 +640,10 @@ static int online_pages_blocks(unsigned long start, unsigned long nr_pages)
 	while (start < end) {
 		order = min(MAX_ORDER - 1,
 			get_order(PFN_PHYS(end) - PFN_PHYS(start)));
+		/* make sure the PFN is aligned and we don't exceed the range */
+		while (!IS_ALIGNED(start, 1ul << order) ||
+		       (1ul << order) > end - start)
+			order--;
 		(*online_page_callback)(pfn_to_page(start), order);
 
 		onlined_pages += (1UL << order);
-- 
2.21.0