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    SubjectRe: [PATCH v8 11/27] x86/mm: Introduce _PAGE_DIRTY_SW
    On Tue, Aug 13, 2019 at 01:52:09PM -0700, Yu-cheng Yu wrote:

    > +static inline pte_t pte_move_flags(pte_t pte, pteval_t from, pteval_t to)
    > +{
    > + if (pte_flags(pte) & from)
    > + pte = pte_set_flags(pte_clear_flags(pte, from), to);
    > + return pte;
    > +}

    Aside of the whole conditional thing (I agree it would be better to have
    this unconditionally); the function doesn't really do as advertised.

    That is, if @from is clear, it doesn't endeavour to make sure @to is
    also clear.

    Now it might be sufficient, but in that case it really needs a comment
    and or different name.

    An implementation that actually moves the bit is something like:

    pteval_t a,b;

    a = native_pte_value(pte);
    b = (a >> from_bit) & 1;
    a &= ~((1ULL << from_bit) | (1ULL << to_bit));
    a |= b << to_bit;
    return make_native_pte(a);

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