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    Subject[PATCH v2 2/4] mm/gup: explicitly define and check internal GUP flags, disallow FOLL_TOUCH
    Date
    Rather than open-coding a list of internal GUP flags in
    is_valid_gup_args(), define which ones are internal.

    In addition, explicitly check to see if the user passed in FOLL_TOUCH
    somehow, as this appears to have been accidentally excluded.

    Reviewed-by: Arnd Bergmann <arnd@arndb.de>
    Reviewed-by: David Hildenbrand <david@redhat.com>
    Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
    ---
    mm/gup.c | 5 ++---
    mm/internal.h | 3 +++
    2 files changed, 5 insertions(+), 3 deletions(-)

    diff --git a/mm/gup.c b/mm/gup.c
    index 2f8a2d89fde1..b21b33d1787e 100644
    --- a/mm/gup.c
    +++ b/mm/gup.c
    @@ -2227,12 +2227,11 @@ static bool is_valid_gup_args(struct page **pages, int *locked,
    /*
    * These flags not allowed to be specified externally to the gup
    * interfaces:
    - * - FOLL_PIN/FOLL_TRIED/FOLL_FAST_ONLY are internal only
    + * - FOLL_TOUCH/FOLL_PIN/FOLL_TRIED/FOLL_FAST_ONLY are internal only
    * - FOLL_REMOTE is internal only and used on follow_page()
    * - FOLL_UNLOCKABLE is internal only and used if locked is !NULL
    */
    - if (WARN_ON_ONCE(gup_flags & (FOLL_PIN | FOLL_TRIED | FOLL_UNLOCKABLE |
    - FOLL_REMOTE | FOLL_FAST_ONLY)))
    + if (WARN_ON_ONCE(gup_flags & INTERNAL_GUP_FLAGS))
    return false;

    gup_flags |= to_set;
    diff --git a/mm/internal.h b/mm/internal.h
    index 449891ad7fdb..499016c6b01d 100644
    --- a/mm/internal.h
    +++ b/mm/internal.h
    @@ -1018,6 +1018,9 @@ enum {
    FOLL_UNLOCKABLE = 1 << 21,
    };

    +#define INTERNAL_GUP_FLAGS (FOLL_TOUCH | FOLL_TRIED | FOLL_REMOTE | FOLL_PIN | \
    + FOLL_FAST_ONLY | FOLL_UNLOCKABLE)
    +
    /*
    * Indicates for which pages that are write-protected in the page table,
    * whether GUP has to trigger unsharing via FAULT_FLAG_UNSHARE such that the
    --
    2.42.0
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