Merge branch 'preempt'

Merge branch 'preempt'

Heiko Carstens says:

====================

The option to select PREEMPT_NONE will go away for all architectures which
support PREEMPT_LAZY [1]. Until now all distributions provide kernels built
with PREEMPT_NONE enabled for s390. In particular this means that all
preempt_disable() / preempt_enable() pairs are optimized away during
compile time.

With PREEMPT_LAZY this is not the case. Switching to PREEMPT_LAZY leads
to a kernel image size increase of ~218kb (defconfig, gcc15).

s390 provides optimized preempt primitives, however there is still room for
improvement. Since support for relocatable lowcore was added access to
preempt_count in lowcore requires an extra call of get_lowcore(), which
generates an extra instruction. Also all instructions have to use a base
register which is not zero to access preempt_count.

Address this by adding a couple of inline assemblies with alternatives.

This generates better code and reduces the size of a PREEMPT_LAZY built
kernel image by ~58kb.

[1] https://lore.kernel.org/all/20251219101502.GB1132199@noisy.programming.kicks-ass.net/

====================

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>