[PATCH v12 0/7] support FEAT_LSUI

Yeoreum Yun
2026-01-21T19:06:28Z

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_LSUI and applies in futex atomic operation
and user_swpX emulation where can replace from ldxr/st{l}xr
pair implmentation with clearing PSTATE.PAN bit to correspondant
load/store unprevileged atomic operation without clearing PSTATE.PAN bit.

This patch based on v6.19-rc6

Patch History
==============
from v11 to v12:
- rebase to v6.19-rc6
- add CONFIG_ARM64_LSUI
- enable LSUI when !CPU_BIG_ENDIAN and PAN presents.
- drop the swp emulation with LSUI insns instead, disable it
when LSUI presents.
- some of small fixes (useless prefix and suffix and etc).
- https://lore.kernel.org/all/20251214112248.901769-1-yeoreum.yun@arm.com/

from v10 to v11:
- rebase to v6.19-rc1
- use cast instruction to emulate deprecated swpb instruction
- https://lore.kernel.org/all/20251103163224.818353-1-yeoreum.yun@arm.com/

from v9 to v10:
- apply FEAT_LSUI to user_swpX emulation.
- add test coverage for LSUI bit in ID_AA64ISAR3_EL1
- rebase to v6.18-rc4
- https://lore.kernel.org/all/20250922102244.2068414-1-yeoreum.yun@arm.com/

from v8 to v9:
- refotoring __lsui_cmpxchg64()
- rebase to v6.17-rc7
- https://lore.kernel.org/all/20250917110838.917281-1-yeoreum.yun@arm.com/

from v7 to v8:
- implements futex_atomic_eor() and futex_atomic_cmpxchg() with casalt
with C helper.
- Drop the small optimisation on ll/sc futex_atomic_set operation.
- modify some commit message.
- https://lore.kernel.org/all/20250816151929.197589-1-yeoreum.yun@arm.com/

from v6 to v7:
- wrap FEAT_LSUI with CONFIG_AS_HAS_LSUI in cpufeature
- remove unnecessary addition of indentation.
- remove unnecessary mte_tco_enable()/disable() on LSUI operation.
- https://lore.kernel.org/all/20250811163635.1562145-1-yeoreum.yun@arm.com/

from v5 to v6:
- rebase to v6.17-rc1
- https://lore.kernel.org/all/20250722121956.1509403-1-yeoreum.yun@arm.com/

from v4 to v5:
- remove futex_ll_sc.h futext_lsui and lsui.h and move them to futex.h
- reorganize the patches.
- https://lore.kernel.org/all/20250721083618.2743569-1-yeoreum.yun@arm.com/

from v3 to v4:
- rebase to v6.16-rc7
- modify some patch's title.
- https://lore.kernel.org/all/20250617183635.1266015-1-yeoreum.yun@arm.com/

from v2 to v3:
- expose FEAT_LSUI to guest
- add help section for LSUI Kconfig
- https://lore.kernel.org/all/20250611151154.46362-1-yeoreum.yun@arm.com/

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

Yeoreum Yun (7):
arm64: Kconfig: add support for LSUI
arm64: cpufeature: add FEAT_LSUI
KVM: arm64: expose FEAT_LSUI to guest
KVM: arm64: kselftest: set_id_regs: add test for FEAT_LSUI
arm64: futex: refactor futex atomic operation
arm64: futex: support futex with FEAT_LSUI
arm64: armv8_deprecated: disable swp emulation when FEAT_LSUI present

arch/arm64/Kconfig | 20 ++
arch/arm64/include/asm/futex.h | 322 +++++++++++++++---
arch/arm64/kernel/armv8_deprecated.c | 16 +
arch/arm64/kernel/cpufeature.c | 27 ++
arch/arm64/kvm/sys_regs.c | 3 +-
arch/arm64/tools/cpucaps | 1 +
.../testing/selftests/kvm/arm64/set_id_regs.c | 1 +
7 files changed, 339 insertions(+), 51 deletions(-)

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