[PATCHv5 09/17] mm/sparse: Check memmap alignment for compound_info_has_mask()

From: Kiryl Shutsemau <kas@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>,
	Muchun Song <muchun.song@linux.dev>,
	David Hildenbrand <david@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	Usama Arif <usamaarif642@gmail.com>,
	Frank van der Linden <fvdl@google.com>
Cc: Oscar Salvador <osalvador@suse.de>,
	Mike Rapoport <rppt@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
	Zi Yan <ziy@nvidia.com>, Baoquan He <bhe@redhat.com>,
	Michal Hocko <mhocko@suse.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Huacai Chen <chenhuacai@kernel.org>,
	WANG Xuerui <kernel@xen0n.name>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	kernel-team@meta.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	loongarch@lists.linux.dev, linux-riscv@lists.infradead.org,
	Kiryl Shutsemau <kas@kernel.org>
Subject: [PATCHv5 09/17] mm/sparse: Check memmap alignment for compound_info_has_mask()
Date: Wed, 28 Jan 2026 13:54:50 +0000	[thread overview]
Message-ID: <20260128135500.22121-10-kas@kernel.org> (raw)
In-Reply-To: <20260128135500.22121-1-kas@kernel.org>

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

Trigger a BUG() for CONFIG_DEBUG_VM=y or WARN() otherwise.

Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Acked-by: Zi Yan <ziy@nvidia.com>
---
 mm/sparse.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/mm/sparse.c b/mm/sparse.c
index b5b2b6f7041b..9c0f4015778c 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -600,6 +600,19 @@ void __init sparse_init(void)
 	BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section)));
 	memblocks_present();
 
+	if (compound_info_has_mask()) {
+		unsigned long alignment;
+		bool aligned;
+
+		alignment = MAX_FOLIO_NR_PAGES * sizeof(struct page);
+		aligned = IS_ALIGNED((unsigned long) pfn_to_page(0), alignment);
+
+		if (IS_ENABLED(CONFIG_DEBUG_VM))
+			BUG_ON(!aligned);
+		else
+			WARN_ON(!aligned);
+	}
+
 	pnum_begin = first_present_section_nr();
 	nid_begin = sparse_early_nid(__nr_to_section(pnum_begin));
 
-- 
2.51.2

