Re: [BOOT-WRAPPER 03/11] aarch64: Implement cpu_init_arch()

[Marc Zyngier <maz@kernel.org>]

On Mon, 29 Jul 2024 17:14:53 +0100,
Mark Rutland <mark.rutland@arm.com> wrote:
> 
> When the boot-wrapper is entered at EL2 it does not initialise
> CNTFRQ_EL0, and in future it may need to initialize other CPU state
> regardless of the exeption level it was entered at.
> 
> Use a common cpu_init_arch() function to initialize CPU state regardless
> of the exception level the boot-wrapper was entered at.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Akos Denke <akos.denke@arm.com>
> Cc: Andre Przywara <andre.przywara@arm.com>
> Cc: Luca Fancellu <luca.fancellu@arm.com>
> Cc: Marc Zyngier <maz@kernel.org>
> ---
>  arch/aarch64/boot.S |  4 +++-
>  arch/aarch64/init.c | 12 +++++++++---
>  2 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/aarch64/boot.S b/arch/aarch64/boot.S
> index 51ef41b..d8d38dd 100644
> --- a/arch/aarch64/boot.S
> +++ b/arch/aarch64/boot.S
> @@ -51,7 +51,7 @@ reset_at_el3:
>  
>  	bl	cpu_init_bootwrapper
>  
> -	bl	cpu_init_el3
> +	bl	cpu_init_arch
>  
>  	bl	gic_secure_init
>  
> @@ -82,6 +82,8 @@ reset_at_el2:
>  
>  	bl	cpu_init_bootwrapper
>  
> +	bl	cpu_init_arch
> +
>  	b	start_bootmethod
>  
>  err_invalid_id:
> diff --git a/arch/aarch64/init.c b/arch/aarch64/init.c
> index c9fc7f1..49abdf7 100644
> --- a/arch/aarch64/init.c
> +++ b/arch/aarch64/init.c
> @@ -52,7 +52,7 @@ static inline bool cpu_has_permission_indirection(void)
>  	return mrs(ID_AA64MMFR3_EL1) & mask;
>  }
>  
> -void cpu_init_el3(void)
> +static void cpu_init_el3(void)
>  {
>  	unsigned long scr = SCR_EL3_RES1 | SCR_EL3_NS | SCR_EL3_HCE;
>  	unsigned long mdcr = 0;
> @@ -153,8 +153,6 @@ void cpu_init_el3(void)
>  
>  		msr(SMCR_EL3, smcr);
>  	}
> -
> -	msr(CNTFRQ_EL0, COUNTER_FREQ);
>  }
>  
>  #ifdef PSCI
> @@ -171,3 +169,11 @@ bool cpu_init_psci_arch(void)
>  	return true;
>  }
>  #endif
> +
> +void cpu_init_arch(void)
> +{
> +	if (mrs(CurrentEL) == CURRENTEL_EL3)
> +		cpu_init_el3();
> +
> +	msr(CNTFRQ_EL0, COUNTER_FREQ);
> +}

Hmmm. This means that you cannot use the BW on a system where EL3 is
implemented, but where you decide to enter at EL2 anyway (the write to
CNTFRQ_EL0 will UNDEF).

I don't care much (I always want the BW to be the first piece of SW to
run), but this is a rather subtle change in behaviour, and we'd better
capture it in the commit message.

With that,

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.