[PATCH 6.12.y 1/2] mm/page_alloc: reject unreasonable folio/compound page sizes in alloc_contig_range_noprof()

[Sasha Levin <sashal@kernel.org>]

From: David Hildenbrand <david@redhat.com>

[ Upstream commit 0bf2edf041dcb0b304a8dbda8c699771d5a245d2 ]

Let's reject them early, which in turn makes folio_alloc_gigantic() reject
them properly.

To avoid converting from order to nr_pages, let's just add MAX_FOLIO_ORDER
and calculate MAX_FOLIO_NR_PAGES based on that.

While at it, let's just make the order a "const unsigned order".

Link: https://lkml.kernel.org/r/20250901150359.867252-7-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: SeongJae Park <sj@kernel.org>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: 4c767c5dd9bc ("mm/page_isolation: guard compound_order() against racing")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/mm.h |  6 ++++--
 mm/page_alloc.c    | 10 +++++++++-
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1728dc3356089..f05962963e28d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2058,11 +2058,13 @@ static inline long folio_nr_pages(const struct folio *folio)
 
 /* Only hugetlbfs can allocate folios larger than MAX_ORDER */
 #ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
-#define MAX_FOLIO_NR_PAGES	(1UL << PUD_ORDER)
+#define MAX_FOLIO_ORDER		PUD_ORDER
 #else
-#define MAX_FOLIO_NR_PAGES	MAX_ORDER_NR_PAGES
+#define MAX_FOLIO_ORDER		MAX_PAGE_ORDER
 #endif
 
+#define MAX_FOLIO_NR_PAGES	(1UL << MAX_FOLIO_ORDER)
+
 /*
  * compound_nr() returns the number of pages in this potentially compound
  * page.  compound_nr() can be called on a tail page, and is defined to
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 480579d7d59e4..887dd3f06a86b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6685,6 +6685,7 @@ static int __alloc_contig_verify_gfp_mask(gfp_t gfp_mask, gfp_t *gfp_cc_mask)
 int alloc_contig_range_noprof(unsigned long start, unsigned long end,
 		       unsigned migratetype, gfp_t gfp_mask)
 {
+	const unsigned int order = ilog2(end - start);
 	unsigned long outer_start, outer_end;
 	int ret = 0;
 
@@ -6699,6 +6700,14 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
 	};
 	INIT_LIST_HEAD(&cc.migratepages);
 
+	/*
+	 * In contrast to the buddy, we allow for orders here that exceed
+	 * MAX_PAGE_ORDER, so we must manually make sure that we are not
+	 * exceeding the maximum folio order.
+	 */
+	if (WARN_ON_ONCE((gfp_mask & __GFP_COMP) && order > MAX_FOLIO_ORDER))
+		return -EINVAL;
+
 	gfp_mask = current_gfp_context(gfp_mask);
 	if (__alloc_contig_verify_gfp_mask(gfp_mask, (gfp_t *)&cc.gfp_mask))
 		return -EINVAL;
@@ -6786,7 +6795,6 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
 			free_contig_range(end, outer_end - end);
 	} else if (start == outer_start && end == outer_end && is_power_of_2(end - start)) {
 		struct page *head = pfn_to_page(start);
-		int order = ilog2(end - start);
 
 		check_new_pages(head, order);
 		prep_new_page(head, order, gfp_mask, 0);
-- 
2.53.0