[PATCH v2 02/10] mm/memory_hotplug: enforce section granularity when onlining/offlining

Already two people (including me) tried to offline subsections, because
the function looks like it can deal with it. But we really can only
online/offline full sections that are properly aligned (e.g., we can only
mark full sections online/offline via SECTION_IS_ONLINE).

Add a simple safety net to document the restriction now. Current users
(core and powernv/memtrace) respect these restrictions.

Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Yang <redacted>
Cc: Baoquan He <redacted>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: David Hildenbrand <redacted>
---
 mm/memory_hotplug.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c781d386d87f9..6856702af68d9 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c

@@ -801,6 +801,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
 	int ret;
 	struct memory_notify arg;
 
+	/* We can only online full sections (e.g., SECTION_IS_ONLINE) */
+	if (WARN_ON_ONCE(!nr_pages ||
+			 !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)))
+		return -EINVAL;
+
 	mem_hotplug_begin();
 
 	/* associate pfn range with the zone */

@@ -1483,6 +1488,11 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 	struct memory_notify arg;
 	char *reason;
 
+	/* We can only offline full sections (e.g., SECTION_IS_ONLINE) */
+	if (WARN_ON_ONCE(!nr_pages ||
+			 !IS_ALIGNED(start_pfn | nr_pages, PAGES_PER_SECTION)))
+		return -EINVAL;
+
 	mem_hotplug_begin();
 
 	/*

-- 
2.26.2