Re: [PATCH v2 6/6] s390/mm: Allow lazy MMU mode disabling

[Alexander Gordeev]

On Thu, Apr 16, 2026 at 07:44:05AM +0200, Heiko Carstens wrote:
> > @@ -169,6 +185,8 @@ void arch_enter_lazy_mmu_mode_for_pte_range(struct mm_struct *mm,
> >  {
> >  	if (!test_facility(13))
> >  		return;
> > +	if (!static_branch_likely(&lazy_mmu))
> > +		return;
> 
> Looks like there is an alternative chicken switch available: remove
> facility bit 13 from the facility list via kernel command line option.
> 
> Unless I am mistaken: that should be sufficient and avoids adding more
> code.

But that would also withdraw multi-IPTE from other unrelated parts of
the code, e.g. from __kernel_map_pages().