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    Subject[PATCH v2 2/9] mm/hugetlb: separate path for hwpoison entry in copy_hugetlb_page_range()
    Date
    From: Naoya Horiguchi <naoya.horiguchi@nec.com>

    Originally copy_hugetlb_page_range() handles migration entries and hwpoisone
    entries in similar manner. But recently the related code path has more code
    for migration entries, and when is_writable_migration_entry() was converted
    to !is_readable_migration_entry(), hwpoison entries on source processes got
    to be unexpectedly updated (which is legitimate for migration entries, but
    not for hwpoison entries). This results in unexpected serious issues like
    kernel panic when foking processes with hwpoison entries in pmd.

    Separate the if branch into one for hwpoison entries and one for migration
    entries.

    Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive")
    Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
    Cc: <stable@vger.kernel.org> # 5.18
    ---
    mm/hugetlb.c | 9 +++++++--
    1 file changed, 7 insertions(+), 2 deletions(-)

    diff --git a/mm/hugetlb.c b/mm/hugetlb.c
    index c538278170a2..f59f43c06601 100644
    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -4784,8 +4784,13 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
    * sharing with another vma.
    */
    ;
    - } else if (unlikely(is_hugetlb_entry_migration(entry) ||
    - is_hugetlb_entry_hwpoisoned(entry))) {
    + } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) {
    + bool uffd_wp = huge_pte_uffd_wp(entry);
    +
    + if (!userfaultfd_wp(dst_vma) && uffd_wp)
    + entry = huge_pte_clear_uffd_wp(entry);
    + set_huge_swap_pte_at(dst, addr, dst_pte, entry, sz);
    + } else if (unlikely(is_hugetlb_entry_migration(entry))) {
    swp_entry_t swp_entry = pte_to_swp_entry(entry);
    bool uffd_wp = huge_pte_uffd_wp(entry);

    --
    2.25.1
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