Re: [PATCH v2 3/6] mm/powerpc/8xx: constify ptep_get() argument

On Tue, Aug 04, 2026 at 02:50:19PM +0200, Christophe Leroy (CS GROUP) wrote:
> Hi Lorenzo,
>
> Le 04/08/2026 à 13:13, Lorenzo Stoakes (ARM) a écrit :
> > On Mon, Aug 03, 2026 at 05:43:57PM +0100, Pedro Falcato wrote:
> > > There is no need for write access to the PTE.
> > >
> > > Signed-off-by: Pedro Falcato <[email protected]>
> >
> > With below addressed LGTM so:
> >
> > Reviewed-by: Lorenzo Stoakes (ARM) <[email protected]>
> >
> > > ---
> > >   arch/powerpc/include/asm/nohash/32/pte-8xx.h | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/arch/powerpc/include/asm/nohash/32/pte-8xx.h b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
> > > index e2ea8ba9f8ca..f2bab31040c7 100644
> > > --- a/arch/powerpc/include/asm/nohash/32/pte-8xx.h
> > > +++ b/arch/powerpc/include/asm/nohash/32/pte-8xx.h
> > > @@ -226,7 +226,7 @@ static inline pte_basic_t pte_update(struct mm_struct *mm, unsigned long addr, p
> > >
> > >   #ifdef CONFIG_PPC_16K_PAGES
> > >   #define ptep_get ptep_get
> > > -static inline pte_t ptep_get(pte_t *ptep)
> > > +static inline pte_t ptep_get(const pte_t *ptep)
> > >   {
> > >   	pte_basic_t val = READ_ONCE(ptep->pte);
> > >   	pte_t pte = {val, val, val, val};
> >
> > Worth making these const too (that {val, val, val, val} horrifies me btw :)?
>
> Any suggestion welcome.

I'm being super nitty, all I mean is:

-   	pte_basic_t val = READ_ONCE(ptep->pte);
-  	pte_t pte = {val, val, val, val};
+   	const pte_basic_t val = READ_ONCE(ptep->pte);
+  	const pte_t pte = {val, val, val, val};

:)

>
> powerpc 8xx page table is independant on page size. When you use 16k pages,
> depending on the address you hit the page for the first time, the HW assist
> page table walk will fetch one of four 4k cells in page table that need to
> be identical as they all four define the same 16k page. Not sure I'm clear.

No that's clear, thanks!

(I say 'horrifying' because I am looking into RCU page table freeing which this
may complicate, though perhaps not in practice, to be continued :)

>
> Christophe
>

--
Cheers, Lorenzo