+ mm-hugetlb-fix-mremap-move-length-truncation.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/hugetlb: fix mremap move length truncation
has been added to the -mm mm-unstable branch.  Its filename is
     mm-hugetlb-fix-mremap-move-length-truncation.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-fix-mremap-move-length-truncation.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Li Zhe <lizhe.67@bytedance.com>
Subject: mm/hugetlb: fix mremap move length truncation
Date: Thu, 22 Oct 2026 11:45:41 +0800

Patch series "mm/hugetlb: fix mremap bugs", v3.

This series fixes a few hugetlb mremap bugs.

Patch 1 fixes the return type of move_hugetlb_page_tables(), so large
hugetlb moves cannot be truncated when reported back to the generic
mremap code.

Patch 2 disables hugetlb PMD sharing for UFFD missing mode, so
UFFDIO_POISON markers cannot become visible through shared PMD page
tables.

Patch 3 fixes the recursive i_mmap_rwsem deadlock in the hugetlb mremap
path by avoiding the destination PMD sharing allocation path while the
mapping lock is already held for write.


This patch (of 3):

move_hugetlb_page_tables() returns the number of bytes moved, but
its return type is int while the generic move_page_tables() path uses
unsigned long lengths.

A hugetlb mremap() move length above INT_MAX can therefore be
misreported to copy_vma_and_data(). The out-of-range conversion to int
is implementation-defined; on common 64-bit builds, for example, a
4 GiB move can be reported as zero, making the caller treat the move as
a failure and use the wrong length for rollback.

Return unsigned long from move_hugetlb_page_tables(), matching
move_page_tables() and preserving the full byte count.

Link: https://lore.kernel.org/20261022034543.51226-1-lizhe.67@bytedance.com
Link: https://lore.kernel.org/20261022034543.51226-2-lizhe.67@bytedance.com
Fixes: 550a7d60bd5e ("mm, hugepages: add mremap() support for hugepage backed vma")
Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Jose A. Perez de Azpillaga <azpijr@gmail.com>
Cc: <stable@vger.kernel.org>
---

 include/linux/hugetlb.h |   15 ++++++---------
 mm/hugetlb.c            |    7 +++----
 2 files changed, 9 insertions(+), 13 deletions(-)

--- a/include/linux/hugetlb.h~mm-hugetlb-fix-mremap-move-length-truncation
+++ a/include/linux/hugetlb.h
@@ -121,10 +121,9 @@ void hugepage_put_subpool(struct hugepag
 
 void hugetlb_dup_vma_private(struct vm_area_struct *vma);
 void clear_vma_resv_huge_pages(struct vm_area_struct *vma);
-int move_hugetlb_page_tables(struct vm_area_struct *vma,
-			     struct vm_area_struct *new_vma,
-			     unsigned long old_addr, unsigned long new_addr,
-			     unsigned long len);
+unsigned long move_hugetlb_page_tables(struct vm_area_struct *vma,
+		struct vm_area_struct *new_vma, unsigned long old_addr,
+		unsigned long new_addr, unsigned long len);
 int copy_hugetlb_page_range(struct mm_struct *, struct mm_struct *,
 			    struct vm_area_struct *, struct vm_area_struct *);
 void unmap_hugepage_range(struct vm_area_struct *,
@@ -338,11 +337,9 @@ static inline int copy_hugetlb_page_rang
 	return 0;
 }
 
-static inline int move_hugetlb_page_tables(struct vm_area_struct *vma,
-					   struct vm_area_struct *new_vma,
-					   unsigned long old_addr,
-					   unsigned long new_addr,
-					   unsigned long len)
+static inline unsigned long move_hugetlb_page_tables(struct vm_area_struct *vma,
+		struct vm_area_struct *new_vma, unsigned long old_addr,
+		unsigned long new_addr, unsigned long len)
 {
 	BUG();
 	return 0;
--- a/mm/hugetlb.c~mm-hugetlb-fix-mremap-move-length-truncation
+++ a/mm/hugetlb.c
@@ -5206,10 +5206,9 @@ static void move_huge_pte(struct vm_area
 	spin_unlock(dst_ptl);
 }
 
-int move_hugetlb_page_tables(struct vm_area_struct *vma,
-			     struct vm_area_struct *new_vma,
-			     unsigned long old_addr, unsigned long new_addr,
-			     unsigned long len)
+unsigned long move_hugetlb_page_tables(struct vm_area_struct *vma,
+		struct vm_area_struct *new_vma, unsigned long old_addr,
+		unsigned long new_addr, unsigned long len)
 {
 	struct hstate *h = hstate_vma(vma);
 	struct address_space *mapping = vma->vm_file->f_mapping;
_

Patches currently in -mm which might be from lizhe.67@bytedance.com are

mm-hugetlb-fix-overbroad-mmu-notifiers-for-unshared-pmds.patch
mm-hugetlb-fix-mremap-move-length-truncation.patch
mm-hugetlb-fix-mremap-deadlock-when-pmd-sharing-is-possible.patch