linux-kernel - Re: [PATCH v9 26/26] arm64: Enable the support of pseudo-NMIs

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Message-ID: <86o981ueyj.wl-marc.zyngier@arm.com>
Date:   Mon, 28 Jan 2019 12:47:00 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Julien Thierry <julien.thierry@....com>
Cc:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <daniel.thompson@...aro.org>,
        <joel@...lfernandes.org>, <christoffer.dall@....com>,
        <james.morse@....com>, <catalin.marinas@....com>,
        <will.deacon@....com>, <mark.rutland@....com>
Subject: Re: [PATCH v9 26/26] arm64: Enable the support of pseudo-NMIs

On Mon, 21 Jan 2019 15:33:45 +0000,
Julien Thierry <julien.thierry@....com> wrote:
> 
> Add a build option and a command line parameter to build and enable the
> support of pseudo-NMIs.
> 
> Signed-off-by: Julien Thierry <julien.thierry@....com>
> Suggested-by: Daniel Thompson <daniel.thompson@...aro.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
>  arch/arm64/Kconfig                              | 14 ++++++++++++++
>  arch/arm64/kernel/cpufeature.c                  | 11 ++++++++++-
>  3 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index b799bcf..173e2cc 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1197,6 +1197,12 @@
>  			to discrete, to make X server driver able to add WB
>  			entry later. This parameter enables that.
>  
> +	enable_pseudo_nmi [ARM64]
> +			Enables support for pseudo-NMIs in the kernel. This
> +			requires both the kernel to be built with
> +			CONFIG_ARM64_PSEUDO_NMI and to be running on a
> +			platform with GICv3.
> +
>  	enable_timer_pin_1 [X86]
>  			Enable PIN 1 of APIC timer
>  			Can be useful to work around chipset bugs
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index a4168d3..8d84bfd 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1328,6 +1328,20 @@ config ARM64_MODULE_PLTS
>  	bool
>  	select HAVE_MOD_ARCH_SPECIFIC
>  
> +config ARM64_PSEUDO_NMI
> +	bool "Support for NMI-like interrupts"
> +	select CONFIG_ARM_GIC_V3
> +	help
> +	  Adds support for mimicking Non-Maskable Interrupts through the use of
> +	  GIC interrupt priority. This support requires version 3 or later of
> +	  Arm GIC.
> +
> +	  This high priority configuration for interrupts need to be

s/need/needs/

> +	  explicitly enabled through the new kernel parameter

It won't be new forever... ;-)

> +	  "enable_pseudo_nmi".

I'm not overly keen on this name. We already have "irqchip.gicv3_nolpi",
so why not adopt something similar. "irqchip.gicv3_pseudo_nmi", taking a
boolean value?

> +
> +	  If unsure, say N
> +
>  config RELOCATABLE
>  	bool
>  	help
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index b530fb24..e66d778 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1207,10 +1207,19 @@ static void cpu_enable_address_auth(struct arm64_cpu_capabilities const *cap)
>  #endif /* CONFIG_ARM64_PTR_AUTH */
>  
>  #ifdef CONFIG_ARM64_PSEUDO_NMI
> +static bool enable_pseudo_nmi;
> +
> +static int __init early_enable_pseudo_nmi(char *p)
> +{
> +	enable_pseudo_nmi = true;

And if you're happy with the above, this becomes:

	return strtobool(p, &enable_pseudo_nmi);

> +	return 0;
> +}
> +early_param("enable_pseudo_nmi", early_enable_pseudo_nmi);
> +
>  static bool can_use_gic_priorities(const struct arm64_cpu_capabilities *entry,
>  				   int scope)
>  {
> -	return false;
> +	return enable_pseudo_nmi && has_useable_gicv3_cpuif(entry, scope);
>  }
>  #endif
>  
> -- 
> 1.9.1
> 

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.