Re: [PATCH v1 06/36] mm/page_alloc: reject unreasonable folio/compound page sizes in alloc_contig_range_noprof()

[David Hildenbrand]

On 29.08.25 02:33, Liam R. Howlett wrote:

* David Hildenbrand <da...@redhat.com> [250827 18:04]:

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.

Reviewed-by: Zi Yan <z...@nvidia.com>
Acked-by: SeongJae Park <s...@kernel.org>
Signed-off-by: David Hildenbrand <da...@redhat.com>

Nit below, but..

Reviewed-by: Liam R. Howlett <liam.howl...@oracle.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 baead29b3e67b..426bc404b80cc 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);

You have changed this from an int to a const unsigned int, which is

totally fine but it was left out of the change log.

Considered to trivial to document, but I can add a sentence about that.

Probably not really
worth mentioning but curious why the change to unsigned here?

orders are always unsigned, like folio_order().

Thanks!

--
Cheers

David / dhildenb