Since Armv9.6, FEAT_LSUI supplies the load/store instructions for
previleged level to access to access user memory without clearing
PSTATE.PAN bit.

This patchset support FEAT_LUSI and applies in futex atomic operation
where can replace from ldxr/stlxr pair implmentation with clearing
PSTATE.PAN bit to correspondant load/store unprevileged atomic operation
without clearing PSTATE.PAN bit.

Patch Sequences
================

Patch #1 adds cpufeature for FEAT_LUSI

Patch #2 expose FEAT_LUSI to guest

Patch #3 adds Kconfig for FEAT_LUSI

Patch #4 separtes former futex atomic-op implmentation from futex.h
to futex_ll_sc_u.h

Patch #5 implments futex atomic operation using lsui instruction.

Patch #6 introduces lsui.h to apply runtime patch to use former
implmentation when FEAT_LUSI doesn't support.

Patch #7 applies lsui.h into arch_futext_atomic_op().

Patch History
==============
from v2 to v3:
  - expose FEAT_LUSI to guest
  - add help section for LUSI Kconfig
  - https://lore.kernel.org/all/20250611151154.46362-1-yeoreum.yun@arm.com/ (local)

from v1 to v2:
  - remove empty v9.6 menu entry
  - locate HAS_LUSI in cpucaps in order
  - https://lore.kernel.org/all/20250611104916.10636-1-yeoreum.yun@arm.com/ (local)

Yeoreum Yun (7):
  arm64: cpufeature: add FEAT_LSUI
  arm64/kvm: expose FEAT_LSUI to guest
  arm64/Kconfig: add LSUI Kconfig
  arm64/futex: move futex atomic logic with clearing PAN bit
  arm64/futex: add futex atomic operation with FEAT_LSUI
  arm64/asm: introduce lsui.h
  arm64/futex: support futex with FEAT_LSUI

 arch/arm64/Kconfig                     |   9 ++
 arch/arm64/include/asm/futex.h         |  99 ++++++-------------
 arch/arm64/include/asm/futex_ll_sc_u.h | 115 +++++++++++++++++++++
 arch/arm64/include/asm/futex_lsui.h    | 132 +++++++++++++++++++++++++
 arch/arm64/include/asm/lsui.h          |  37 +++++++
 arch/arm64/kernel/cpufeature.c         |   8 ++
 arch/arm64/kvm/sys_regs.c              |   5 +-
 arch/arm64/tools/cpucaps               |   1 +
 8 files changed, 336 insertions(+), 70 deletions(-)
 create mode 100644 arch/arm64/include/asm/futex_ll_sc_u.h
 create mode 100644 arch/arm64/include/asm/futex_lsui.h
 create mode 100644 arch/arm64/include/asm/lsui.h

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