[merged mm-stable] scatterlist-disallow-non-contigous-page-ranges-in-a-single-sg-entry.patch removed from -mm tree

[merged mm-stable] scatterlist-disallow-non-contigous-page-ranges-in-a-single-sg-entry.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: scatterlist: disallow non-contigous page ranges in a single SG entry
has been removed from the -mm tree.  Its filename was
     scatterlist-disallow-non-contigous-page-ranges-in-a-single-sg-entry.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: scatterlist: disallow non-contigous page ranges in a single SG entry
Date: Mon, 1 Sep 2025 17:03:45 +0200

The expectation is that there is currently no user that would pass in
non-contigous page ranges: no allocator, not even VMA, will hand these
out.

The only problematic part would be if someone would provide a range
obtained directly from memblock, or manually merge problematic ranges.  If
we find such cases, we should fix them to create separate SG entries.

Let's check in sg_set_page() that this is really the case.  No need to
check in sg_set_folio(), as pages in a folio are guaranteed to be
contiguous.  As sg_set_page() gets inlined into modules, we have to export
the page_range_contiguous() helper -- use EXPORT_SYMBOL, there is nothing
special about this helper such that we would want to enforce GPL-only
modules.

We can now drop the nth_page() usage in sg_page_iter_page().

Link: https://lkml.kernel.org/r/20250901150359.867252-25-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/scatterlist.h |    3 ++-
 mm/util.c                   |    1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

--- a/include/linux/scatterlist.h~scatterlist-disallow-non-contigous-page-ranges-in-a-single-sg-entry
+++ a/include/linux/scatterlist.h
@@ -158,6 +158,7 @@ static inline void sg_assign_page(struct
 static inline void sg_set_page(struct scatterlist *sg, struct page *page,
 			       unsigned int len, unsigned int offset)
 {
+	VM_WARN_ON_ONCE(!page_range_contiguous(page, ALIGN(len + offset, PAGE_SIZE) / PAGE_SIZE));
 	sg_assign_page(sg, page);
 	sg->offset = offset;
 	sg->length = len;
@@ -600,7 +601,7 @@ void __sg_page_iter_start(struct sg_page
  */
 static inline struct page *sg_page_iter_page(struct sg_page_iter *piter)
 {
-	return nth_page(sg_page(piter->sg), piter->sg_pgoffset);
+	return sg_page(piter->sg) + piter->sg_pgoffset;
 }
 
 /**
--- a/mm/util.c~scatterlist-disallow-non-contigous-page-ranges-in-a-single-sg-entry
+++ a/mm/util.c
@@ -1315,4 +1315,5 @@ bool page_range_contiguous(const struct
 			return false;
 	return true;
 }
+EXPORT_SYMBOL(page_range_contiguous);
 #endif
_

Patches currently in -mm which might be from david@redhat.com are