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

From: Julien Thierry <julien.thierry@arm.com>
To: Marc Zyngier <marc.zyngier@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, daniel.thompson@linaro.org,
	joel@joelfernandes.org, christoffer.dall@arm.com,
	james.morse@arm.com, catalin.marinas@arm.com,
	will.deacon@arm.com, mark.rutland@arm.com
Subject: Re: [PATCH v9 26/26] arm64: Enable the support of pseudo-NMIs
Date: Wed, 30 Jan 2019 13:46:57 +0000	[thread overview]
Message-ID: <38589cbc-dbaf-b903-6c56-65e796063680@arm.com> (raw)
In-Reply-To: <86o981ueyj.wl-marc.zyngier@arm.com>

On 28/01/2019 12:47, Marc Zyngier wrote:
> On Mon, 21 Jan 2019 15:33:45 +0000,
> Julien Thierry <julien.thierry@arm.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@arm.com>
>> Suggested-by: Daniel Thompson <daniel.thompson@linaro.org>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will.deacon@arm.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... ;-)
> 

Good point!

>> +	  "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?
> 

Sure, I'm fine with that.

>> +
>> +	  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);
> 

Thanks,

-- 
Julien Thierry