linux-kernel - Re: [PATCH 1/2] arm64: booting.rst: Clarify on requiring non-secure EL2

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Message-ID: <YdhoZPfjuI9vxSe3@FVFF77S0Q05N>
Date:   Fri, 7 Jan 2022 16:20:52 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Andre Przywara <andre.przywara@....com>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] arm64: booting.rst: Clarify on requiring non-secure
 EL2

On Fri, Jan 07, 2022 at 04:00:55PM +0000, Andre Przywara wrote:
> The ARMv8.4 architecture revision introduced the EL2 exception level
> to the secure world. Clarify the existing wording to make sure that
> Linux relies on being executed in the non-secure state.
> 
> Signed-off-by: Andre Przywara <andre.przywara@....com>
> ---
>  Documentation/arm64/booting.rst | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/arm64/booting.rst b/Documentation/arm64/booting.rst
> index 52d060caf8bb..07cb34ed4200 100644
> --- a/Documentation/arm64/booting.rst
> +++ b/Documentation/arm64/booting.rst
> @@ -10,9 +10,9 @@ This document is based on the ARM booting document by Russell King and
>  is relevant to all public releases of the AArch64 Linux kernel.
>  
>  The AArch64 exception model is made up of a number of exception levels
> -(EL0 - EL3), with EL0 and EL1 having a secure and a non-secure
> -counterpart.  EL2 is the hypervisor level and exists only in non-secure
> -mode. EL3 is the highest priority level and exists only in secure mode.
> +(EL0 - EL3), with EL0, EL1 and EL2 having a secure and a non-secure
> +counterpart.  EL2 is the hypervisor level, EL3 is the highest priority
> +level and exists only in secure mode. Both are architecturally optional.
>  
>  For the purposes of this document, we will use the term `boot loader`
>  simply to define all software that executes on the CPU(s) before control
> @@ -167,8 +167,8 @@ Before jumping into the kernel, the following conditions must be met:
>  
>    All forms of interrupts must be masked in PSTATE.DAIF (Debug, SError,
>    IRQ and FIQ).
> -  The CPU must be in either EL2 (RECOMMENDED in order to have access to
> -  the virtualisation extensions) or non-secure EL1.
> +  The CPU must be in non-secure state, either in EL2 (RECOMMENDED in order
> +  to have access  to the virtualisation extensions), or in EL1.
                   ^^

Nit: double space

It might be clearer to explicitly say "non-secure EL2" and "non-secure EL1"
here, but either way this looks good to me, so with the whitespace fixed:

Reviewed-by: Mark Rutland <mark.rutland@....com>

Thanks,
Mark.