Re: [PATCH v1 01/11] arm/pgtable: define PFN_PTE_SHIFT on arm and arm64

[David Hildenbrand]

On 23.01.24 12:38, Ryan Roberts wrote:
> On 23/01/2024 11:31, David Hildenbrand wrote:
> > > > > If high bits are used for
> > > > > something else, then we might produce a garbage PTE on overflow, but that
> > > > > shouldn't really matter I concluded for folio_pte_batch() purposes, we'd not
> > > > > detect "belongs to this folio batch" either way.
> > > >
> > > > Exactly.
> > > >
> > > > > Maybe it's likely cleaner to also have a custom pte_next_pfn() on ppc, I just
> > > > > hope that we don't lose any other arbitrary PTE bits by doing the pte_pgprot().
> > > >
> > > > I don't see the need for ppc to implement pte_next_pfn().
> > >
> > > Agreed.
> >
> > So likely we should then do on top for powerpc (whitespace damage):
> >
> > diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> > index a04ae4449a025..549a440ed7f65 100644
> > --- a/arch/powerpc/mm/pgtable.c
> > +++ b/arch/powerpc/mm/pgtable.c
> > @@ -220,10 +220,7 @@ void set_ptes(struct mm_struct *mm, unsigned long addr,
> > pte_t *ptep,
> >                          break;
> >                  ptep++;
> >                  addr += PAGE_SIZE;
> > -               /*
> > -                * increment the pfn.
> > -                */
> > -               pte = pfn_pte(pte_pfn(pte) + 1, pte_pgprot((pte)));
> > +               pte = pte_next_pfn(pte);
> >          }
> >   }
>
> Looks like commit 47b8def9358c ("powerpc/mm: Avoid calling
> arch_enter/leave_lazy_mmu() in set_ptes") changed from doing the simple
> increment to this more complex approach, but the log doesn't say why.

@Aneesh, was that change on purpose?

--
Cheers,

David / dhildenb