linux-kernel - Re: [PATCH v3 0/7] support FEAT_LSUI and apply it on futex atomic ops

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Message-ID: <aFz9N1Bs6Y5f1sCT@e129823.arm.com>
Date: Thu, 26 Jun 2025 08:56:39 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: catalin.marinas@....com, will@...nel.org, broonie@...nel.org,
	oliver.upton@...ux.dev, ardb@...nel.org, frederic@...nel.org,
	james.morse@....com, joey.gouly@....com,
	scott@...amperecomputing.com
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/7] support FEAT_LSUI and apply it on futex atomic ops

Gentle ping in case of forgotten.

> 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/
>
> 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/
>
> 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
>
> --
> LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
>

--
Sincerely,
Yeoreum Yun