[PATCH] riscv/mm: Add soft-dirty page tracking support

[Alexandre Ghiti]

Hi Chunyan,

On 10/07/2024 05:30, Chunyan Zhang wrote:
> The PTE bit (9) is reserved for software, so we can use it for
> soft-dirty tracking. This patch adds its standard handlers for
> PTE, PMD, and swap entry.


Unfortunately, ZONE_DEVICE has just used this last bit and should be 
merged in 6.11.

I'm currently discussing internally how we can get 2 other PTE bits from 
RVI in order to have the same number of available bits as x86 and arm64. 
I guess that for now, if we really have a usecase for softdirty (and I 
think we do with CRIU), we'll have to make ZONE_DEVICE and softdirty 
mutually exclusive.


>
> To add swap PTE soft-dirty tracking, we borrow bit (4) which is
> available for swap PTEs on RISC-V systems.
>
> This patch has been tested with the kselftest mm suite in which
> soft-dirty and madv_populate run and pass, and no regressions
> are observed in any of the other tests.


Did you give CRIU a try?

Thanks,

Alex


>
> Signed-off-by: Chunyan Zhang <zhangchunyan at iscas.ac.cn>
> ---
>   arch/riscv/Kconfig                    |  1 +
>   arch/riscv/include/asm/pgtable-bits.h | 13 ++++++
>   arch/riscv/include/asm/pgtable.h      | 65 ++++++++++++++++++++++++++-
>   3 files changed, 78 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index b94176e25be1..2e3ad2925a6b 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -118,6 +118,7 @@ config RISCV
>   	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
>   	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
>   	select HAVE_ARCH_SECCOMP_FILTER
> +	select HAVE_ARCH_SOFT_DIRTY
>   	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
>   	select HAVE_ARCH_TRACEHOOK
>   	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
> diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
> index 179bd4afece4..bab48f5fd1e2 100644
> --- a/arch/riscv/include/asm/pgtable-bits.h
> +++ b/arch/riscv/include/asm/pgtable-bits.h
> @@ -19,6 +19,19 @@
>   #define _PAGE_SOFT      (3 << 8)    /* Reserved for software */
>   
>   #define _PAGE_SPECIAL   (1 << 8)    /* RSW: 0x1 */
> +
> +#ifdef CONFIG_MEM_SOFT_DIRTY
> +#define _PAGE_SOFT_DIRTY	(1 << 9)    /* RSW: 0x2 for software dirty tracking */
> +/*
> + * BIT 4 is not involved into swap entry computation, so we
> + * can borrow it for swap page soft-dirty tracking.
> + */
> +#define _PAGE_SWP_SOFT_DIRTY	_PAGE_USER
> +#else
> +#define _PAGE_SOFT_DIRTY	0
> +#define _PAGE_SWP_SOFT_DIRTY	0
> +#endif /* CONFIG_MEM_SOFT_DIRTY */
> +
>   #define _PAGE_TABLE     _PAGE_PRESENT
>   
>   /*
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index aad8b8ca51f1..46f512f52580 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -408,7 +408,7 @@ static inline pte_t pte_mkwrite_novma(pte_t pte)
>   
>   static inline pte_t pte_mkdirty(pte_t pte)
>   {
> -	return __pte(pte_val(pte) | _PAGE_DIRTY);
> +	return __pte(pte_val(pte) | _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
>   }
>   
>   static inline pte_t pte_mkclean(pte_t pte)
> @@ -436,6 +436,36 @@ static inline pte_t pte_mkhuge(pte_t pte)
>   	return pte;
>   }
>   
> +static inline int pte_soft_dirty(pte_t pte)
> +{
> +	return pte_val(pte) & _PAGE_SOFT_DIRTY;
> +}
> +
> +static inline pte_t pte_mksoft_dirty(pte_t pte)
> +{
> +	return __pte(pte_val(pte) | _PAGE_SOFT_DIRTY);
> +}
> +
> +static inline pte_t pte_clear_soft_dirty(pte_t pte)
> +{
> +	return __pte(pte_val(pte) & ~(_PAGE_SOFT_DIRTY));
> +}
> +
> +static inline int pte_swp_soft_dirty(pte_t pte)
> +{
> +	return pte_val(pte) & _PAGE_SWP_SOFT_DIRTY;
> +}
> +
> +static inline pte_t pte_swp_mksoft_dirty(pte_t pte)
> +{
> +	return __pte(pte_val(pte) | _PAGE_SWP_SOFT_DIRTY);
> +}
> +
> +static inline pte_t pte_swp_clear_soft_dirty(pte_t pte)
> +{
> +	return __pte(pte_val(pte) & ~(_PAGE_SWP_SOFT_DIRTY));
> +}
> +
>   #ifdef CONFIG_RISCV_ISA_SVNAPOT
>   #define pte_leaf_size(pte)	(pte_napot(pte) ?				\
>   					napot_cont_size(napot_cont_order(pte)) :\
> @@ -721,6 +751,38 @@ static inline pmd_t pmd_mkdirty(pmd_t pmd)
>   	return pte_pmd(pte_mkdirty(pmd_pte(pmd)));
>   }
>   
> +static inline int pmd_soft_dirty(pmd_t pmd)
> +{
> +	return pte_soft_dirty(pmd_pte(pmd));
> +}
> +
> +static inline pmd_t pmd_mksoft_dirty(pmd_t pmd)
> +{
> +	return pte_pmd(pte_mksoft_dirty(pmd_pte(pmd)));
> +}
> +
> +static inline pmd_t pmd_clear_soft_dirty(pmd_t pmd)
> +{
> +	return pte_pmd(pte_clear_soft_dirty(pmd_pte(pmd)));
> +}
> +
> +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> +static inline int pmd_swp_soft_dirty(pmd_t pmd)
> +{
> +	return pte_swp_soft_dirty(pmd_pte(pmd));
> +}
> +
> +static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd)
> +{
> +	return pte_pmd(pte_swp_mksoft_dirty(pmd_pte(pmd)));
> +}
> +
> +static inline pmd_t pmd_swp_clear_soft_dirty(pmd_t pmd)
> +{
> +	return pte_pmd(pte_swp_clear_soft_dirty(pmd_pte(pmd)));
> +}
> +#endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */
> +
>   static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
>   				pmd_t *pmdp, pmd_t pmd)
>   {
> @@ -811,6 +873,7 @@ extern pmd_t pmdp_collapse_flush(struct vm_area_struct *vma,
>    * Format of swap PTE:
>    *	bit            0:	_PAGE_PRESENT (zero)
>    *	bit       1 to 3:       _PAGE_LEAF (zero)
> + *	bit            4:	_PAGE_SWP_SOFT_DIRTY
>    *	bit            5:	_PAGE_PROT_NONE (zero)
>    *	bit            6:	exclusive marker
>    *	bits      7 to 11:	swap type