[PATCH RFC 06/35] mm/page_alloc: reject unreasonable folio/compound page sizes in alloc_contig_range_noprof()

David Hildenbrand
2025-08-21T20:07:33Z

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.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
include/linux/mm.h | 6 ++++--
mm/page_alloc.c | 5 ++++-
2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 00c8a54127d37..77737cbf2216a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2055,11 +2055,13 @@ 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 ca9e6b9633f79..1e6ae4c395b30 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6833,6 +6833,7 @@ 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,
acr_flags_t alloc_flags, gfp_t gfp_mask)
{
+ const unsigned int order = ilog2(end - start);
unsigned long outer_start, outer_end;
int ret = 0;

@@ -6850,6 +6851,9 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
PB_ISOLATE_MODE_CMA_ALLOC :
PB_ISOLATE_MODE_OTHER;

+ 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;
@@ -6947,7 +6951,6 @@ 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);
--
2.50.1