arm64: futex: Support futex with FEAT_LSUI

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Current futex atomic operations are implemented using LL/SC instructions
while temporarily clearing PSTATE.PAN and setting PSTATE.TCO (if
KASAN_HW_TAGS is enabled). With Armv9.6, FEAT_LSUI provides atomic
instructions for user memory access in the kernel without the need for
PSTATE bits toggling.

Use the FEAT_LSUI instructions to implement the futex atomic operations.
Note that some futex operations do not have a matching LSUI instruction,
(eor or word-sized cmpxchg). For such cases, use cas{al}t to implement
the operation.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
[catalin.marinas@arm.com: add comment on -EAGAIN in __lsui_futex_cmpxchg()]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

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Yeoreum Yun 2026-03-14 17:51:30 +00:00 • committed by Catalin Marinas

parent eaa3babcce

commit 44adf2bf40

2 changed files with 185 additions and 2 deletions

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160

arch/arm64/include/asm/futex.h

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27

arch/arm64/include/asm/lsui.h

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