Re: [PATCH v2 1/1] s390/mm: Fix handling of _PAGE_UNUSED pte bit

[Heiko Carstens <hca@linux.ibm.com>]

On Mon, Jun 15, 2026 at 12:31:03PM +0200, Claudio Imbrenda wrote:
> On Mon, 15 Jun 2026 11:43:00 +0200
> Heiko Carstens <hca@linux.ibm.com> wrote:
> 
> [...]
> 
> > > @@ -175,6 +179,8 @@ pte_t ptep_modify_prot_start(struct
> vm_area_struct *vma, unsigned long addr,
> > >  void ptep_modify_prot_commit(struct vm_area_struct *vma, unsigned long addr,
> > >  			     pte_t *ptep, pte_t old_pte, pte_t pte)
> > >  {
> > > +	if (pte_present(pte))
> > > +		pte = clear_pte_bit(pte, __pgprot(_PAGE_UNUSED));
> > >  	set_pte(ptep, pte);  
> > 
> > Can't we move the logic from set_ptes() to set_pte() instead? The above
> 
> set_pte() is also used for things that are not ptes, and in those cases
> we probably don't want to touch that bit, although technically it is
> currently unused for present large pmds and puds.

I can only see huge_pte_clear() for this.

If that's the only user I'd rather add a BUG_ON() there instead of starting to
sprinkle the logic around. This _will_ break sooner or later.