Re: [PATCH v7 2/4] s390/mm: Batch PTE updates in lazy MMU mode

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

On Thu, Oct 01, 2026 at 05:41:18PM +0200, Heiko Carstens wrote:
> On Thu, Oct 01, 2026 at 11:20:17AM +0200, Alexander Gordeev wrote:
> > On Thu, Oct 01, 2026 at 10:21:43AM +0200, Heiko Carstens wrote:
> > > On Thu, Oct 01, 2026 at 10:00:55AM +0200, Alexander Gordeev wrote:
> > > > On Mon, Aug 24, 2026 at 12:40:48PM +0200, Heiko Carstens wrote:
> > > Not really. But why is lazy_mmu_count 32 bit? Do you expect a nesting
> > > level of 2^32? :) If you would reduce that to one byte you could use
> > > tmy or cliy.
> > 
> > Good point. But still, do you think it worth dropping the KASAN check?
> 
> KASAN check for lowcore? I don't think we care - this is initialized to zero
> anyway, so what could go wrong? Also given how frequently these operations are
> used, yes, please drop KASAN checks.

Of course you could still add an explicit KASAN/KCSAN check by adding an
instrument_read() call (see e.g. s390's fpu-insn.h, which has plenty of them).

But why do you think that would be helpful for a lowcore field, where it is
known that is initialized to zero? What am I missing?