[PATCHv4 07/14] mm/sparse: Check memmap alignment for compound_info_has_mask()

[Kiryl Shutsemau <kas@kernel.org>]

If page->compound_info encodes a mask, it is expected that memmap to be
naturally aligned to the maximum folio size.

Add a warning if it is not.

A warning is sufficient as MAX_FOLIO_ORDER is very rarely used, so the
kernel is still likely to be functional if this strict check fails.

Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
---
 include/linux/mmzone.h | 1 +
 mm/sparse.c            | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 390ce11b3765..7e4f69b9d760 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -91,6 +91,7 @@
 #endif
 
 #define MAX_FOLIO_NR_PAGES	(1UL << MAX_FOLIO_ORDER)
+#define MAX_FOLIO_SIZE		(PAGE_SIZE << MAX_FOLIO_ORDER)
 
 enum migratetype {
 	MIGRATE_UNMOVABLE,
diff --git a/mm/sparse.c b/mm/sparse.c
index 17c50a6415c2..5f41a3edcc24 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -600,6 +600,11 @@ void __init sparse_init(void)
 	BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));
 	memblocks_present();
 
+	if (compound_info_has_mask()) {
+		WARN_ON(!IS_ALIGNED((unsigned long)pfn_to_page(0),
+				    MAX_FOLIO_SIZE / sizeof(struct page)));
+	}
+
 	pnum_begin = first_present_section_nr();
 	nid_begin = sparse_early_nid(__nr_to_section(pnum_begin));
 
-- 
2.51.2