FAILED: patch "[PATCH] mm/hugetlb_vmemmap: fix __hugetlb_vmemmap_optimize_folios()" failed to apply to 6.18-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 6e25c6a9c7eff141ecfc966ecdb7801db2a8810e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026090320-cufflink-ambitious-4582@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 6e25c6a9c7eff141ecfc966ecdb7801db2a8810e Mon Sep 17 00:00:00 2001
From: Muchun Song <muchun.song@linux.dev>
Date: Fri, 12 Jun 2026 11:58:46 +0800
Subject: [PATCH] mm/hugetlb_vmemmap: fix __hugetlb_vmemmap_optimize_folios()

__hugetlb_vmemmap_optimize_folios() uses incorrect arguments when handling
bootmem HugeTLB folios.

The section number passed to register_page_bootmem_memmap() is derived
from the vmemmap virtual address of folio->page instead of the folio PFN,
so the bootmem memmap metadata can be registered against the wrong
section.  The helper is also given HUGETLB_VMEMMAP_RESERVE_SIZE even
though it expects a page count, not a size in bytes.  In addition, the
write-protect range is based on pages_per_huge_page(h), which does not
cover the full HugeTLB vmemmap area and can leave part of the shared tail
vmemmap mapping writable.

Fix the section lookup to use folio_pfn(folio), use
HUGETLB_VMEMMAP_RESERVE_PAGES when registering the reserved memmap pages,
and use hugetlb_vmemmap_size(h) for the write-protect range.

Link: https://lore.kernel.org/20260612035903.2468601-3-songmuchun@bytedance.com
Fixes: 752fe17af693 ("mm/hugetlb: add pre-HVO framework")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Frank van der Linden <fvdl@google.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador (SUSE) <osalvador@kernel.org>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index c713c0d2593a..ea6af85bfec1 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -635,12 +635,12 @@ static void __hugetlb_vmemmap_optimize_folios(struct hstate *h,
 			 * mirrored tail page structs RO.
 			 */
 			spfn = (unsigned long)&folio->page;
-			epfn = spfn + pages_per_huge_page(h);
+			epfn = spfn + hugetlb_vmemmap_size(h);
 			vmemmap_wrprotect_hvo(spfn, epfn, folio_nid(folio),
 					HUGETLB_VMEMMAP_RESERVE_SIZE);
-			register_page_bootmem_memmap(pfn_to_section_nr(spfn),
+			register_page_bootmem_memmap(pfn_to_section_nr(folio_pfn(folio)),
 					&folio->page,
-					HUGETLB_VMEMMAP_RESERVE_SIZE);
+					HUGETLB_VMEMMAP_RESERVE_PAGES);
 			continue;
 		}