On 01.09.25 17:03, David Hildenbrand wrote:

Let's disallow handing out PFN ranges with non-contiguous pages, so we
can remove the nth-page usage in __cma_alloc(), and so any callers don't
have to worry about that either when wanting to blindly iterate pages.

This is really only a problem in configs with SPARSEMEM but without
SPARSEMEM_VMEMMAP, and only when we would cross memory sections in some
cases.

Will this cause harm? Probably not, because it's mostly 32bit that does
not support SPARSEMEM_VMEMMAP. If this ever becomes a problem we could
look into allocating the memmap for the memory sections spanned by a
single CMA region in one go from memblock.

Reviewed-by: Alexandru Elisei <redacted>
Reviewed-by: Lorenzo Stoakes <redacted>
Signed-off-by: David Hildenbrand <redacted>
---

@Andrew, the following fixup on top. I'm still cross-compiling it, but
at the time you read this mail my cross compiles should have been done.


 From cbfa2763e1820b917ce3430f45e5f3a55eb2970f Mon Sep 17 00:00:00 2001
From: David Hildenbrand <redacted>
Date: Tue, 9 Sep 2025 05:50:13 -0400
Subject: [PATCH] fixup: mm/cma: refuse handing out non-contiguous page ranges

Apparently we can have NUMMU configs with SPARSEMEM enabled.

Signed-off-by: David Hildenbrand <redacted>
---
  mm/util.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/util.c b/mm/util.c
index 248f877f629b6..6c1d64ed02211 100644
--- a/mm/util.c
+++ b/mm/util.c

@@ -1306,6 +1306,7 @@ unsigned int folio_pte_batch(struct folio *folio, pte_t *ptep, pte_t pte,
  {
  	return folio_pte_batch_flags(folio, NULL, ptep, &pte, max_nr, 0);
  }
+#endif /* CONFIG_MMU */
  
  #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
  /**

@@ -1342,4 +1343,3 @@ bool page_range_contiguous(const struct page *page, unsigned long nr_pages)
  }
  EXPORT_SYMBOL(page_range_contiguous);
  #endif
-#endif /* CONFIG_MMU */

-- 
2.50.1


-- 
Cheers

David / dhildenb