linux-kernel - Re: [PATCH v3 10/47] arm64: mpam: Initialise and context switch the MPAMSM

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Message-ID: <aWk7Pyai4AcoQc_J@arm.com>
Date: Thu, 15 Jan 2026 19:08:47 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Ben Horgan <ben.horgan@....com>
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
	baolin.wang@...ux.alibaba.com, carl@...amperecomputing.com,
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Subject: Re: [PATCH v3 10/47] arm64: mpam: Initialise and context switch the
 MPAMSM_EL1 register

On Mon, Jan 12, 2026 at 04:58:37PM +0000, Ben Horgan wrote:
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 0cdfb3728f43..2ede543b3eeb 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -2491,6 +2491,8 @@ cpu_enable_mpam(const struct arm64_cpu_capabilities *entry)
>  		regval = READ_ONCE(per_cpu(arm64_mpam_current, cpu));
>  
>  	write_sysreg_s(regval, SYS_MPAM1_EL1);
> +	if (system_supports_sme())
> +		write_sysreg_s(regval & (MPAMSM_EL1_PARTID_D | MPAMSM_EL1_PMG_D), SYS_MPAMSM_EL1);
>  	isb();

Do we know for sure that system_supports_sme() returns true at this
point (if SME supported)? Digging into the code, system_supports_sme()
uses alternative_has_cap_unlikely() which relies on instruction
patching. setup_system_capabilities(), IIUC, patches the alternatives
after enable_cpu_capabilities(). I think you better use cpus_have_cap().

-- 
Catalin