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    Subject[PATCH 5.15 15/21] mm: fix missing cache flush for all tail pages of compound page
    Date
    From: Muchun Song <songmuchun@bytedance.com>

    commit 2771739a7162782c0aa6424b2e3dd874e884a15d upstream.

    The D-cache maintenance inside move_to_new_page() only consider one
    page, there is still D-cache maintenance issue for tail pages of
    compound page (e.g. THP or HugeTLB).

    THP migration is only enabled on x86_64, ARM64 and powerpc, while
    powerpc and arm64 need to maintain the consistency between I-Cache and
    D-Cache, which depends on flush_dcache_page() to maintain the
    consistency between I-Cache and D-Cache.

    But there is no issues on arm64 and powerpc since they already considers
    the compound page cache flushing in their icache flush function.
    HugeTLB migration is enabled on arm, arm64, mips, parisc, powerpc,
    riscv, s390 and sh, while arm has handled the compound page cache flush
    in flush_dcache_page(), but most others do not.

    In theory, the issue exists on many architectures. Fix this by not
    using flush_dcache_folio() since it is not backportable.

    Link: https://lkml.kernel.org/r/20220210123058.79206-3-songmuchun@bytedance.com
    Fixes: 290408d4a250 ("hugetlb: hugepage migration core")
    Signed-off-by: Muchun Song <songmuchun@bytedance.com>
    Reviewed-by: Zi Yan <ziy@nvidia.com>
    Cc: Axel Rasmussen <axelrasmussen@google.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Fam Zheng <fam.zheng@bytedance.com>
    Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Lars Persson <lars.persson@axis.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: Peter Xu <peterx@redhat.com>
    Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    mm/migrate.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -948,9 +948,12 @@ static int move_to_new_page(struct page
    if (!PageMappingFlags(page))
    page->mapping = NULL;

    - if (likely(!is_zone_device_page(newpage)))
    - flush_dcache_page(newpage);
    + if (likely(!is_zone_device_page(newpage))) {
    + int i, nr = compound_nr(newpage);

    + for (i = 0; i < nr; i++)
    + flush_dcache_page(newpage + i);
    + }
    }
    out:
    return rc;

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