Re: [PATCH 1/6] arm64: insn: remove deprecated memory barrier types

[Vladimir Murzin <vladimir.murzin@arm.com>]

Hi Ada,

On 9/28/26 14:30, Ada Couprie Diaz wrote:
> Arm ARM DDI 0487 version M.c[0] deprecated a number of types
> used as options for the DMB and DSB instructions, with no change
> in behaviour.
> The deprecated types are not used in the kernel, so remove them
> from our instruction generation framework and add the missing
> `AARCH64_INSN_MB_OSH` case in `__get_barrier_crm_val()`.
> 

Arm ARM says that OSH has the same behaviour as SY, so I'd assume
any user of OSH should be fine to upgrade to SY, no?

> This simplifies the switch-case and now covers all the enum types,
> which allows for making the DSB and DMB generation non instrumentable
> in a follow-up commit.
> 
> [0]: https://support.arm.com/documentation/ddi0487/mc/
>      (See C6.2.150, C6.2.152)
> 
> Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> ---
>  arch/arm64/include/asm/insn.h |  6 ------
>  arch/arm64/lib/insn.c         | 10 ++--------
>  2 files changed, 2 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
> index 1ce75a4426387..8ec9d86cc575c 100644
> --- a/arch/arm64/include/asm/insn.h
> +++ b/arch/arm64/include/asm/insn.h
> @@ -302,14 +302,8 @@ enum aarch64_insn_mb_type {
>  	AARCH64_INSN_MB_ST,
>  	AARCH64_INSN_MB_LD,
>  	AARCH64_INSN_MB_ISH,
> -	AARCH64_INSN_MB_ISHST,
> -	AARCH64_INSN_MB_ISHLD,
>  	AARCH64_INSN_MB_NSH,
> -	AARCH64_INSN_MB_NSHST,
> -	AARCH64_INSN_MB_NSHLD,
>  	AARCH64_INSN_MB_OSH,
> -	AARCH64_INSN_MB_OSHST,
> -	AARCH64_INSN_MB_OSHLD,
>  };
>  
>  #define	__AARCH64_INSN_FUNCS(abbr, mask, val)				\
> diff --git a/arch/arm64/lib/insn.c b/arch/arm64/lib/insn.c
> index e70ac02385153..c70820d65805f 100644
> --- a/arch/arm64/lib/insn.c
> +++ b/arch/arm64/lib/insn.c
> @@ -1572,16 +1572,10 @@ static u32 __get_barrier_crm_val(enum aarch64_insn_mb_type type)
>  		return 0xd;
>  	case AARCH64_INSN_MB_ISH:
>  		return 0xb;
> -	case AARCH64_INSN_MB_ISHST:
> -		return 0xa;
> -	case AARCH64_INSN_MB_ISHLD:
> -		return 0x9;
>  	case AARCH64_INSN_MB_NSH:
>  		return 0x7;
> -	case AARCH64_INSN_MB_NSHST:
> -		return 0x6;
> -	case AARCH64_INSN_MB_NSHLD:
> -		return 0x5;
> +	case AARCH64_INSN_MB_OSH:
> +		return 0x3;
>  	default:
>  		pr_err("%s: unknown barrier type %d\n", __func__, type);
>  		return AARCH64_BREAK_FAULT;
> -- 2.43.0
> 

It looks like NSH, ISH and OSH applies to DSB and deprecated in case of DMB
which is slightly confusing. Given that we drop bunch of encodings perhaps we
can inline logic in aarch64_insn_gen_d{m,s}b()?

Cheers
Vladimir