Re: [PATCH] riscv: enable HAVE_CMPXCHG_{DOUBLE,LOCAL}

["Miquel Sabaté Solà" <mssola@mssola.com>]

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Miquel Sabaté Solà @ 2026-02-20 08:44 +01:

> Support for atomic Compare-And-Swap instructions has been in the RISC-V
> port of the Linux kernel for a long time. That being said, we apparently
> never bothered to set HAVE_CMPXCHG_DOUBLE and HAVE_CMPXCHG_LOCAL in the
> Kconfig, despite having all the framework to support them.
>
> Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>
> ---
> I have built this patch with multiple configurations and ran it with KVM
> (the VisionFive2 board that I have lacks the needed extensions). All seems
> to work, but I do wonder if we did not enable these for a reason or this
> just slipped through. So far in the code I believe everything is in place,
> and I haven't seen any commit in the git log stating otherwise.
>
>  Documentation/features/locking/cmpxchg-local/arch-support.txt | 2 +-
>  arch/riscv/Kconfig                                            | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/features/locking/cmpxchg-local/arch-support.txt b/Documentation/features/locking/cmpxchg-local/arch-support.txt
> index 2c3a4b91f16d..28d5fa8c3b4f 100644
> --- a/Documentation/features/locking/cmpxchg-local/arch-support.txt
> +++ b/Documentation/features/locking/cmpxchg-local/arch-support.txt
> @@ -20,7 +20,7 @@
>      |    openrisc: | TODO |
>      |      parisc: | TODO |
>      |     powerpc: | TODO |
> -    |       riscv: | TODO |
> +    |       riscv: |  ok  |
>      |        s390: |  ok  |
>      |          sh: | TODO |
>      |       sparc: | TODO |
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 7e76b6316425..7c6726a8d738 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -151,6 +151,8 @@ config RISCV
>  	select HAVE_ARCH_USERFAULTFD_WP if 64BIT && MMU && USERFAULTFD && RISCV_ISA_SVRSW60T59B
>  	select HAVE_ARCH_VMAP_STACK if MMU && 64BIT
>  	select HAVE_ASM_MODVERSIONS
> +	select HAVE_CMPXCHG_DOUBLE if RISCV_ISA_ZACAS && RISCV_ISA_ZABHA
> +	select HAVE_CMPXCHG_LOCAL if RISCV_ISA_ZACAS && RISCV_ISA_ZABHA
>  	select HAVE_CONTEXT_TRACKING_USER
>  	select HAVE_DEBUG_KMEMLEAK
>  	select HAVE_DMA_CONTIGUOUS if MMU

Gentle ping :)

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