Re: [PATCH v1] riscv: support arch_has_hw_pte_young()

[Yong-Xuan Wang]

Hi Jinyu,

It seems like it has been a while since the last release of this patch. Do
you have any plans for the patch recently? Or, do you mind sharing any
internal progress on the patch?

We are starting to work on the Svadu extension of pte A/D bit feature on
Linux. Do you find any places where we may potentially work together to
get things moving? Also, I am willing to base on top of your work and
continue sending the series (by keeping all the credits from the original
work)

Please let me know if you have any thoughts, thanks :)

Regards,
Yong-Xuan

On Sun, Jan 29, 2023 at 2:53 PM Jinyu Tang <tjytimi@xxxxxxx> wrote:
>
> The arch_has_hw_pte_young() is false for riscv by default. If it's
> false, page table walk is almost skipped for MGLRU reclaim. And it
> will also cause useless step in __wp_page_copy_user().
>
> RISC-V Privileged Book says that riscv have two schemes to manage A
> and D bit.
>
> So add a config for selecting, the default is true. For simple
> implementation riscv CPU which just generate page fault, unselect it.
>
> Signed-off-by: Jinyu Tang <tjytimi@xxxxxxx>
> ---
>  arch/riscv/Kconfig               | 10 ++++++++++
>  arch/riscv/include/asm/pgtable.h |  7 +++++++
>  2 files changed, 17 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index e2b656043abf..17c82885549c 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -180,6 +180,16 @@ config PAGE_OFFSET
>         default 0x80000000 if 64BIT && !MMU
>         default 0xff60000000000000 if 64BIT
>
> +config ARCH_HAS_HARDWARE_PTE_YOUNG
> +       bool "Hardware Set PTE Access Bit"
> +       default y
> +       help
> +         Select if hardware set A bit when PTE is accessed. The default is
> +         'Y', because most RISC-V CPU hardware can manage A and D bit.
> +         But RISC-V may have simple implementation that do not support
> +         hardware set A bit but only generate page fault, for that case just
> +         unselect it.
> +
>  config KASAN_SHADOW_OFFSET
>         hex
>         depends on KASAN_GENERIC
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 4eba9a98d0e3..1db54ab4e1ba 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -532,6 +532,13 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
>          */
>         return ptep_test_and_clear_young(vma, address, ptep);
>  }
> +#ifdef CONFIG_ARCH_HAS_HARDWARE_PTE_YOUNG
> +#define arch_has_hw_pte_young arch_has_hw_pte_young
> +static inline bool arch_has_hw_pte_young(void)
> +{
> +       return true;
> +}
> +#endif
>
>  #define pgprot_noncached pgprot_noncached
>  static inline pgprot_t pgprot_noncached(pgprot_t _prot)
> --
> 2.30.2
>
>
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