The quilt patch titled Subject: mm: userfaultfd: correct dirty flags set for both present and swap pte has been removed from the -mm tree. Its filename was mm-userfaultfd-correct-dirty-flags-set-for-both-present-and-swap-pte.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------ From: Barry Song v-songbaohua@oppo.com Subject: mm: userfaultfd: correct dirty flags set for both present and swap pte Date: Fri, 9 May 2025 10:09:12 +1200
As David pointed out, what truly matters for mremap and userfaultfd move operations is the soft dirty bit. The current comment and implementation���which always sets the dirty bit for present PTEs and fails to set the soft dirty bit for swap PTEs���are incorrect. This could break features like Checkpoint-Restore in Userspace (CRIU).
This patch updates the behavior to correctly set the soft dirty bit for both present and swap PTEs in accordance with mremap.
Link: https://lkml.kernel.org/r/20250508220912.7275-1-21cnbao@gmail.com Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") Signed-off-by: Barry Song v-songbaohua@oppo.com Reported-by: David Hildenbrand david@redhat.com Closes: https://lore.kernel.org/linux-mm/02f14ee1-923f-47e3-a994-4950afb9afcc@redhat... Acked-by: Peter Xu peterx@redhat.com Reviewed-by: Suren Baghdasaryan surenb@google.com Cc: Lokesh Gidra lokeshgidra@google.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/userfaultfd.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
--- a/mm/userfaultfd.c~mm-userfaultfd-correct-dirty-flags-set-for-both-present-and-swap-pte +++ a/mm/userfaultfd.c @@ -1064,8 +1064,13 @@ static int move_present_pte(struct mm_st src_folio->index = linear_page_index(dst_vma, dst_addr);
orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot); - /* Follow mremap() behavior and treat the entry dirty after the move */ - orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma); + /* Set soft dirty bit so userspace can notice the pte was moved */ +#ifdef CONFIG_MEM_SOFT_DIRTY + orig_dst_pte = pte_mksoft_dirty(orig_dst_pte); +#endif + if (pte_dirty(orig_src_pte)) + orig_dst_pte = pte_mkdirty(orig_dst_pte); + orig_dst_pte = pte_mkwrite(orig_dst_pte, dst_vma);
set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte); out: @@ -1100,6 +1105,9 @@ static int move_swap_pte(struct mm_struc }
orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); +#ifdef CONFIG_MEM_SOFT_DIRTY + orig_src_pte = pte_swp_mksoft_dirty(orig_src_pte); +#endif set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); double_pt_unlock(dst_ptl, src_ptl);
_
Patches currently in -mm which might be from v-songbaohua@oppo.com are