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

Alexander Gordeev
2026-04-16T07:01:13Z

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().