[PATCH v4 00/11] s390: More this_cpu_*() changes

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

v4:
- With the change to la instead of agrk also the register pair cannot be
  mapped to gpr0/gpr1 anymore, since all three registers involved in pcpu
  operations are now used as base or index registers. If gpr0 is used as
  base or index register the corresponding instructions treat the content
  of that register as zero, instead of using its real content. Fix that
  by using the "a" instead if "d" constraint for register pairs. Also add
  another sanity check to cover this. [Sashiko]

v3:
- Add various sanity checks to enforce correct register usage
  [Mark Rutland]

- Use %N instead of %M operand modifier to access odd register of a
  register pair in inline assemblies. Strictly speaking this is not
  correct, since %N is supposed to be used for DImode operands and %M for
  TImode operands. However both gcc and clang handle them identical, and
  there is an existing user of %N in the kernel since many years.
  Therefore use %N to get rid of the not yet released clang 24
  dependency. [Christian Borntraeger]

- Use la (load address) instruction with base and index register to
  generate a CPUs percpu variable address instead of agrk. la is
  available for all architecture levels. This removes the z196
  dependency as minimum architecture level. [Christian Borntraeger]

- Change coding style at some places, and fix various typos in commit
  messages and comments.

- Fix compile error caused by missing semicolon.

v2:
- Yet another brown paper bug: Re-add CPU migration check to last
  patch. Unconditionally recalculating and updating the percpu variable
  address and percpu offset register can corrupt previous context
  register state in several cases (not only the single case reported by
  Sashiko).

v1:
Most of this is only about cleaning up the percpu code after preemptible
this_cpu_*() operations have been implemented. The first ten patches are
all more or less trivial cleanup patches trying to make the code shorter
and more readable.

The only non-trivial patch is the last one, which converts s390's
this_cpu_*() operations to use a similar scheme like Mark Rutland
provided it for arm64 [1]. This allows to simplify the irq entry and exit
path, however at the cost of slightly worse code for this_cpu_*()
operations.

The simplified irq entry and exit code seems to be worth it. Usable
performance numbers are not available yet, however I don't expect big
difference to before.

[1] https://lore.kernel.org/all/20260904161758.376504-1-mark.rutland@arm.com/

Thanks,
Heiko

Heiko Carstens (11):
  s390/percpu: Fix comment typo
  s390/percpu: Add sanity check to GEN_MVIY macro
  s390/lowcore: Remove _AC() from LOWCORE_ALT_ADDRESS
  s390/percpu: Let MVIY_PERCPU() calculate alternative displacement
  s390/percpu/lowcore: Add and use LC_PERCPU lowcore offset defines
  s390/percpu: Rename inline assembly symbolic names
  s390/percpu: Use __PCPU_BEGIN() and __PCPU_END() for inline assemblies
  s390/percpu: Use percpu code section for this_cpu_cmpxchg128()
  s390/percpu: Use percpu code section for this_cpu_xchg()
  s390/percpu: Use percpu code section for this_cpu_cmpxchg()
  s390/percpu: Rework to simplify percpu_entry() and percpu_exit()

 arch/s390/include/asm/entry-percpu.h |  71 ++----
 arch/s390/include/asm/lowcore.h      |   5 +-
 arch/s390/include/asm/percpu.h       | 354 +++++++++++++++++----------
 arch/s390/kernel/irq.c               |  10 +-
 arch/s390/kernel/nmi.c               |   4 +-
 arch/s390/kernel/traps.c             |   4 +-
 6 files changed, 248 insertions(+), 200 deletions(-)

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2.53.0