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    SubjectRe: [RFC 1/4] arm64/mm: Add SW and HW dirty state helpers
    On 07.07.23 07:33, Anshuman Khandual wrote:
    > This factors out low level SW and HW state changes i.e make and clear into
    > separate helpers making them explicit improving readability. This also adds
    > pte_rdonly() helper as well. No functional change is intended.
    >
    > Cc: Catalin Marinas <catalin.marinas@arm.com>
    > Cc: Will Deacon <will@kernel.org>
    > Cc: linux-arm-kernel@lists.infradead.org
    > Cc: linux-kernel@vger.kernel.org
    > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
    > ---
    > arch/arm64/include/asm/pgtable.h | 52 ++++++++++++++++++++++++++------
    > 1 file changed, 42 insertions(+), 10 deletions(-)
    >
    > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
    > index 0bd18de9fd97..fb03be697819 100644
    > --- a/arch/arm64/include/asm/pgtable.h
    > +++ b/arch/arm64/include/asm/pgtable.h
    > @@ -103,6 +103,7 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
    > #define pte_young(pte) (!!(pte_val(pte) & PTE_AF))
    > #define pte_special(pte) (!!(pte_val(pte) & PTE_SPECIAL))
    > #define pte_write(pte) (!!(pte_val(pte) & PTE_WRITE))
    > +#define pte_rdonly(pte) (!!(pte_val(pte) & PTE_RDONLY))
    > #define pte_user(pte) (!!(pte_val(pte) & PTE_USER))
    > #define pte_user_exec(pte) (!(pte_val(pte) & PTE_UXN))
    > #define pte_cont(pte) (!!(pte_val(pte) & PTE_CONT))
    > @@ -120,7 +121,7 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
    > (__boundary - 1 < (end) - 1) ? __boundary : (end); \
    > })
    >
    > -#define pte_hw_dirty(pte) (pte_write(pte) && !(pte_val(pte) & PTE_RDONLY))
    > +#define pte_hw_dirty(pte) (pte_write(pte) && !pte_rdonly(pte))
    > #define pte_sw_dirty(pte) (!!(pte_val(pte) & PTE_DIRTY))
    > #define pte_dirty(pte) (pte_sw_dirty(pte) || pte_hw_dirty(pte))
    >
    > @@ -174,6 +175,39 @@ static inline pmd_t clear_pmd_bit(pmd_t pmd, pgprot_t prot)
    > return pmd;
    > }
    >
    > +static inline pte_t pte_hw_mkdirty(pte_t pte)

    I'd have called this "pte_mkhw_dirty", similar to "pte_mksoft_dirty".

    > +{
    > + if (pte_write(pte))
    > + pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY));
    > +
    > + return pte;
    > +}
    > +
    > +static inline pte_t pte_sw_mkdirty(pte_t pte)

    pte_mksw_dirty

    > +{
    > + return set_pte_bit(pte, __pgprot(PTE_DIRTY));
    > +}
    > +
    > +static inline __always_unused pte_t pte_hw_clr_dirty(pte_t pte)

    pte_clear_hw_dirty (again, similar to pte_clear_soft_dirty )

    > +{
    > + return set_pte_bit(pte, __pgprot(PTE_RDONLY));
    > +}
    > +
    > +static inline pte_t pte_sw_clr_dirty(pte_t pte)

    pte_clear_sw_dirty

    > +{
    > + pte = clear_pte_bit(pte, __pgprot(PTE_DIRTY));
    > +
    > + /*
    > + * Clearing the software dirty state requires clearing
    > + * the PTE_DIRTY bit along with setting the PTE_RDONLY
    > + * ensuring a page fault on subsequent write access.
    > + *
    > + * NOTE: Setting the PTE_RDONLY (as a coincident) also
    > + * implies clearing the HW dirty state.
    > + */
    > + return set_pte_bit(pte, __pgprot(PTE_RDONLY));
    > +}
    > +
    > static inline pmd_t set_pmd_bit(pmd_t pmd, pgprot_t prot)
    > {
    > pmd_val(pmd) |= pgprot_val(prot);
    > @@ -189,19 +223,17 @@ static inline pte_t pte_mkwrite(pte_t pte)
    >
    > static inline pte_t pte_mkclean(pte_t pte)
    > {
    > - pte = clear_pte_bit(pte, __pgprot(PTE_DIRTY));
    > - pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
    > -
    > - return pte;
    > + /*
    > + * Subsequent call to pte_hw_clr_dirty() is not required
    > + * because pte_sw_clr_dirty() in turn does that as well.
    > + */
    > + return pte_sw_clr_dirty(pte);

    Hm, I'm not sure if that simplifies things.

    You call pte_sw_clr_dirty() and suddenly your hw dirty bit is clear?

    In that case I think the current implementation is clearer: it doesn't
    provide primitives that don't make any sense.

    > }
    >
    > static inline pte_t pte_mkdirty(pte_t pte)
    > {
    > - pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));
    > -
    > - if (pte_write(pte))
    > - pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY));
    > -
    > + pte = pte_sw_mkdirty(pte);
    > + pte = pte_hw_mkdirty(pte);

    That looks weird. Especially, pte_hw_mkdirty() only does something if
    pte_write().

    Shouldn't pte_hw_mkdirty() bail out if it cannot do anything reasonable
    (IOW, !writable)?

    > return pte;
    > }
    >

    --
    Cheers,

    David / dhildenb

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