Re: [PATCH v2 2/3] RISC-V: mm: Enable huge page support to kernel_page_present() function

[Andrew Jones]

On Tue, Jan 10, 2023 at 06:45:19AM +0000, JeeHeng Sia wrote:
> 
> 
> > -----Original Message-----
> > From: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> > Sent: Monday, 9 January, 2023 10:45 PM
> > To: JeeHeng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>
> > Cc: 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 v2 2/3] RISC-V: mm: Enable huge page support to
> > kernel_page_present() function
> > 
> > On Mon, Jan 09, 2023 at 02:24:06PM +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.
> > >
> > > 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..73fdec8c0a72 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(*pud))
> >                       ^ p4d
> > 
> > I guess you got lucky with the stack garbage in your testing.
> You are right. But the reason it is added here is because kernel page table walk is checking for the p4d_leaf as well. 
> For example: walk_p4d_range() in the mm/pagewalk.c. So, I just trying to make it consistent to the Kernel page table walk mechanism.
> Should I remove it?

The only thing I see wrong with it is the use of the uninitialized
pointer. Just change 'pud' to 'p4d'.

Thanks,
drew

> > 
> > > +		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
> > >
> > 
> > Thanks,
> > drew