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 <20230127091051.1465278-4-jeeheng.sia@starfivetech.com> <Y9g9XGzF/X3OwXdP@spud>
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From:   Alexandre Ghiti <alexghiti@rivosinc.com>
Date:   Tue, 31 Jan 2023 09:19:08 +0100
Message-ID: <CAHVXubh2P5TxdMsbW2TY7NxemSFX81UuvgO9schnTEBvzuAn2Q@mail.gmail.com>
Subject: Re: [PATCH v3 3/4] RISC-V: mm: Enable huge page support to
 kernel_page_present() function
To:     Conor Dooley <conor@kernel.org>
Cc:     Sia Jee Heng <jeeheng.sia@starfivetech.com>,
        paul.walmsley@sifive.com, palmer@dabbelt.com,
        aou@eecs.berkeley.edu, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org, leyfoon.tan@starfivetech.com,
        mason.huo@starfivetech.com
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Precedence: bulk

Hi,

On Mon, Jan 30, 2023 at 10:57 PM Conor Dooley <conor@kernel.org> wrote:
>
> +CC Alex
>
> On Fri, Jan 27, 2023 at 05:10:50PM +0800, Sia Jee Heng wrote:
> > Currently kernel_page_present() function doesn't support huge page
> > detection causes the function to mistakenly return false to the
> > hibernation core.
>
> This sounds like a bug & should have a fixes tag, no? I assume for
> whatever commit enabled huge page support...
> We don't support set_memory, which by the looks of things is the other
> usecase for this function, so probably doesn't need backporting.

Maybe add this patch in the Fixes tag: commit 9e953cda5cdf ("riscv:
Introduce huge page support for 32/64bit kernel").

>
> Alex, does this change look good to you?

Yes, just one thing though: what about a pgd_leaf() test? Even if very
unlikely (I see x86 does not even test it), the privileged spec states
it is possible to have a 256TB page.

Thanks,

Alex

>
> > Add huge page detection to the function to solve the problem.
> >
> > Signed-off-by: Sia Jee Heng <jeeheng.sia@starfivetech.com>
> > Reviewed-by: Ley Foon Tan <leyfoon.tan@starfivetech.com>
> > Reviewed-by: Mason Huo <mason.huo@starfivetech.com>
> > ---
> >  arch/riscv/mm/pageattr.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
> > index 86c56616e5de..792b8d10cdfc 100644
> > --- a/arch/riscv/mm/pageattr.c
> > +++ b/arch/riscv/mm/pageattr.c
> > @@ -221,14 +221,20 @@ bool kernel_page_present(struct page *page)
> >       p4d = p4d_offset(pgd, addr);
> >       if (!p4d_present(*p4d))
> >               return false;
> > +     if (p4d_leaf(*p4d))
> > +             return true;
> >
> >       pud = pud_offset(p4d, addr);
> >       if (!pud_present(*pud))
> >               return false;
> > +     if (pud_leaf(*pud))
> > +             return true;
> >
> >       pmd = pmd_offset(pud, addr);
> >       if (!pmd_present(*pmd))
> >               return false;
> > +     if (pmd_leaf(*pmd))
> > +             return true;
> >
> >       pte = pte_offset_kernel(pmd, addr);
> >       return pte_present(*pte);
> > --
> > 2.34.1
> >