[RFC PATCH 24/36] arm64: booting: Document boot requirements for FEAT_NMI

[Jinjie Ruan]

On 7/9/2026 8:13 PM, Vladimir Murzin wrote:
> From: Mark Brown <broonie at kernel.org>
> 
> In order to use FEAT_NMI we must be able to use ALLINT, require that
> it behave as though not trapped when it is present.
> 
> Signed-off-by: Mark Brown <broonie at kernel.org>
> Signed-off-by: Ada Couprie Diaz <ada.coupriediaz at arm.com>
> Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
> ---
>  Documentation/arch/arm64/booting.rst | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/arch/arm64/booting.rst b/Documentation/arch/arm64/booting.rst
> index 13ef311dace8..3170b26ae981 100644
> --- a/Documentation/arch/arm64/booting.rst
> +++ b/Documentation/arch/arm64/booting.rst
> @@ -568,6 +568,12 @@ Before jumping into the kernel, the following conditions must be met:
>  
>      - HCRX_EL2.EnASR (bit 2) must be initialised to 0b1.
>  
> +  For CPUs with support for Non-maskable Interrupts (FEAT_NMI):
> +
> +  - If the kernel is entered at EL1 and EL2 is present:
> +
> +    - HCRX_EL2.TALLINT (bit 6) must be initialised to 0b0.
> +

Reviewed-by: Jinjie Ruan <ruanjinjie at huawei.com>

>  The requirements described above for CPU mode, caches, MMUs, architected
>  timers, coherency and system registers apply to all CPUs.  All CPUs must
>  enter the kernel in the same exception level.  Where the values documented