linux-kernel - Re: [PATCH v1] riscv: support arch_has_hw_pte_young()

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Message-ID: <CAMWQL2h3OTeiV=P+LOp2FwJsc8SKTUH1gi3gYTGDdhP+KNQpdw@mail.gmail.com>
Date:   Mon, 28 Aug 2023 15:26:01 +0800
From:   Yong-Xuan Wang <yongxuan.wang@...ive.com>
To:     Alexandre Ghiti <alex@...ti.fr>
Cc:     Jinyu Tang <tjytimi@....com>, palmer@...osinc.com,
        paul.walmsley@...ive.com, palmer@...belt.com, yuzhao@...gle.com,
        conor.dooley@...rochip.com, ajones@...tanamicro.com,
        guoren@...nel.org, tongtiangen@...wei.com, anup@...infault.org,
        akpm@...ux-foundation.org, falcon@...ylab.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Greentime Hu <greentime.hu@...ive.com>,
        Vincent Chen <vincent.chen@...ive.com>
Subject: Re: [PATCH v1] riscv: support arch_has_hw_pte_young()

Hi Alex,

On Sat, Aug 26, 2023 at 3:39 AM Alexandre Ghiti <alex@...ti.fr> wrote:
>
> 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?
>
>

Yes, that's fine with me. Thank you!

Regards,
Yong-Xuan

> 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@....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@....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
> >>
> >>
> >> _______________________________________________
> >> linux-riscv mailing list
> >> linux-riscv@...ts.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-riscv
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv

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