Re: [PATCH] x86/mm/pti: in pti_clone_pgtable() don't increase addr by PUD_SIZE

Rik van Riel
2019-08-20T13:22:11Z

On Tue, 2019-08-20 at 13:16 +0200, Thomas Gleixner wrote:
> On Tue, 20 Aug 2019, Peter Zijlstra wrote:
> > What that code wants to do is skip to the end of the pud, a
> > pmd_size
> > increase will not do that. And right below this, there's a second
> > instance of this exact pattern.
> >
> > Did I get the below right?
> >
> > ---
> > diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
> > index b196524759ec..32b20b3cb227 100644
> > --- a/arch/x86/mm/pti.c
> > +++ b/arch/x86/mm/pti.c
> > @@ -330,12 +330,14 @@ pti_clone_pgtable(unsigned long start,
> > unsigned long end,
> >
> > pud = pud_offset(p4d, addr);
> > if (pud_none(*pud)) {
> > + addr &= PUD_MASK;
> > addr += PUD_SIZE;
>
> round_up(addr, PUD_SIZE);
>
> perhaps?

Won't that keep returning the same address forever
if addr & PUD_MASK == 0?