RE: [PATCH v3 3/4] RISC-V: mm: Enable huge page support to kernel_page_present() function

[JeeHeng Sia]

> -----Original Message-----
> From: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> Sent: Tuesday, 31 January, 2023 4:19 PM
> To: Conor Dooley <conor@xxxxxxxxxx>
> Cc: JeeHeng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>; paul.walmsley@xxxxxxxxxx; palmer@xxxxxxxxxxx; aou@xxxxxxxxxxxxxxxxx; linux-
> riscv@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Leyfoon Tan <leyfoon.tan@xxxxxxxxxxxxxxxx>; Mason Huo
> <mason.huo@xxxxxxxxxxxxxxxx>
> Subject: Re: [PATCH v3 3/4] RISC-V: mm: Enable huge page support to kernel_page_present() function
> 
> Hi,
> 
> On Mon, Jan 30, 2023 at 10:57 PM Conor Dooley <conor@xxxxxxxxxx> 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").
Sure, will add the fixes tag.
> 
> >
> > 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.
I can add it in. But as you are probably aware that x86 and ARM don't even tested it. Thanks.
> 
> Thanks,
> 
> Alex
> 
> >
> > > Add huge page detection to the function to solve the problem.
> > >
> > > Signed-off-by: Sia Jee Heng <jeeheng.sia@xxxxxxxxxxxxxxxx>
> > > Reviewed-by: Ley Foon Tan <leyfoon.tan@xxxxxxxxxxxxxxxx>
> > > Reviewed-by: Mason Huo <mason.huo@xxxxxxxxxxxxxxxx>
> > > ---
> > >  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
> > >