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    SubjectRe: [PATCH 2/6] arm64: pgtable: Ensure dirty bit is preserved across pte_wrprotect()
    On Fri, Nov 20, 2020 at 02:35:53PM +0000, Will Deacon wrote:
    > 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>

    It this stable material if it would be a problem once ARM64 supports
    softdirty in future?

    > Signed-off-by: Will Deacon <will@kernel.org>
    > ---
    > arch/arm64/include/asm/pgtable.h | 27 ++++++++++++++-------------
    > 1 file changed, 14 insertions(+), 13 deletions(-)
    >
    > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
    > index 1bdf51f01e73..a155551863c9 100644
    > --- a/arch/arm64/include/asm/pgtable.h
    > +++ b/arch/arm64/include/asm/pgtable.h
    > @@ -162,13 +162,6 @@ static inline pmd_t set_pmd_bit(pmd_t pmd, pgprot_t prot)
    > return pmd;
    > }
    >
    > -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));
    > @@ -194,6 +187,20 @@ static inline pte_t pte_mkdirty(pte_t pte)
    > 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));
    > @@ -843,12 +850,6 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
    > 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));
    > --
    > 2.29.2.454.gaff20da3a2-goog
    >

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