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    Subject[PATCH 5.4 20/98] arm64: pgtable: Ensure dirty bit is preserved across pte_wrprotect()
    Date
    From: Will Deacon <will@kernel.org>

    commit ff1712f953e27f0b0718762ec17d0adb15c9fd0b upstream.

    With hardware dirty bit management, calling pte_wrprotect() on a writable,
    dirty PTE will lose the dirty state and return a read-only, clean entry.

    Move the logic from ptep_set_wrprotect() into pte_wrprotect() to ensure that
    the dirty bit is preserved for writable entries, as this is required for
    soft-dirty bit management if we enable it in the future.

    Cc: <stable@vger.kernel.org>
    Fixes: 2f4b829c625e ("arm64: Add support for hardware updates of the access and dirty pte bits")
    Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
    Link: https://lore.kernel.org/r/20201120143557.6715-3-will@kernel.org
    Signed-off-by: Will Deacon <will@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm64/include/asm/pgtable.h | 27 ++++++++++++++-------------
    1 file changed, 14 insertions(+), 13 deletions(-)

    --- a/arch/arm64/include/asm/pgtable.h
    +++ b/arch/arm64/include/asm/pgtable.h
    @@ -136,13 +136,6 @@ static inline pte_t set_pte_bit(pte_t pt
    return pte;
    }

    -static inline pte_t pte_wrprotect(pte_t pte)
    -{
    - pte = clear_pte_bit(pte, __pgprot(PTE_WRITE));
    - pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
    - return pte;
    -}
    -
    static inline pte_t pte_mkwrite(pte_t pte)
    {
    pte = set_pte_bit(pte, __pgprot(PTE_WRITE));
    @@ -168,6 +161,20 @@ static inline pte_t pte_mkdirty(pte_t pt
    return pte;
    }

    +static inline pte_t pte_wrprotect(pte_t pte)
    +{
    + /*
    + * If hardware-dirty (PTE_WRITE/DBM bit set and PTE_RDONLY
    + * clear), set the PTE_DIRTY bit.
    + */
    + if (pte_hw_dirty(pte))
    + pte = pte_mkdirty(pte);
    +
    + pte = clear_pte_bit(pte, __pgprot(PTE_WRITE));
    + pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
    + return pte;
    +}
    +
    static inline pte_t pte_mkold(pte_t pte)
    {
    return clear_pte_bit(pte, __pgprot(PTE_AF));
    @@ -783,12 +790,6 @@ static inline void ptep_set_wrprotect(st
    pte = READ_ONCE(*ptep);
    do {
    old_pte = pte;
    - /*
    - * If hardware-dirty (PTE_WRITE/DBM bit set and PTE_RDONLY
    - * clear), set the PTE_DIRTY bit.
    - */
    - if (pte_hw_dirty(pte))
    - pte = pte_mkdirty(pte);
    pte = pte_wrprotect(pte);
    pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep),
    pte_val(old_pte), pte_val(pte));

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