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Date: Thu,  4 Apr 2024 10:17:26 -0700
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Message-ID: <20240404171726.2302435-1-lokeshgidra@google.com>
Subject: [PATCH] userfaultfd: change src_folio after ensuring it's unpinned in UFFDIO_MOVE
From: Lokesh Gidra <lokeshgidra@google.com>
To: akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, surenb@google.com, 
	kernel-team@android.com, aarcange@redhat.com, peterx@redhat.com, 
	david@redhat.com, zhengqi.arch@bytedance.com, kaleshsingh@google.com, 
	ngeoffray@google.com, Lokesh Gidra <lokeshgidra@google.com>
Content-Type: text/plain; charset="UTF-8"

Commit d7a08838ab74 ("mm: userfaultfd: fix unexpected change to src_folio
when UFFDIO_MOVE fails") moved the src_folio->{mapping, index} changing
to after clearing the page-table and ensuring that it's not pinned. This
avoids failure of swapout+migration and possibly memory corruption.

However, the commit missed fixing it in the huge-page case.

Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
---
 mm/huge_memory.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9859aa4f7553..89f58c7603b2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2259,9 +2259,6 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm
 			goto unlock_ptls;
 		}
 
-		folio_move_anon_rmap(src_folio, dst_vma);
-		WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
-
 		src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd);
 		/* Folio got pinned from under us. Put it back and fail the move. */
 		if (folio_maybe_dma_pinned(src_folio)) {
@@ -2270,6 +2267,9 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm
 			goto unlock_ptls;
 		}
 
+		folio_move_anon_rmap(src_folio, dst_vma);
+		WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
+
 		_dst_pmd = mk_huge_pmd(&src_folio->page, dst_vma->vm_page_prot);
 		/* Follow mremap() behavior and treat the entry dirty after the move */
 		_dst_pmd = pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma);
-- 
2.44.0.478.gd926399ef9-goog