[PATCH v1] riscv: support arch_has_hw_pte_young()

[Alexandre Ghiti]

Hi Yong-Xuan,


On 25/08/2023 07:42, Yong-Xuan Wang wrote:
> 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.


This task was assigned to me on the RISE kernel spreadsheet, if you 
indeed take over, I'll change it to your name: any objection?


Thanks,


Alex


> 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 at 163.com> 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 at 163.com>
>> ---
>>   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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