Re: [boot-wrapper 3/3] aarch64: Enable access into RCW[S]MASK_EL1 registers from EL2 and below

[Mark Rutland <mark.rutland@arm.com>]

On Tue, Jul 23, 2024 at 04:36:30PM +0530, Anshuman Khandual wrote:
> FEAT_THE adds RCW[S]MASK_EL1 system registers. But access into these system
> registers from EL2 and below trap to EL3 unless SCR_EL3.RCWMASKEn is set.
> 
> Enable access to RCW[S]MASK_EL1 registers when they are implemented.

This looks fine.

IIUC we don't need to initialize these new registers as they only affect
the behaviour of new instructions which we don't expect SW to use until
privileged SW has configured these registers (as they reset to UNKNOWN
values even at the highest implemented EL).

Mark.

> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
>  arch/aarch64/include/asm/cpu.h | 2 ++
>  arch/aarch64/init.c            | 3 +++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/arch/aarch64/include/asm/cpu.h b/arch/aarch64/include/asm/cpu.h
> index 57d66e4..8404152 100644
> --- a/arch/aarch64/include/asm/cpu.h
> +++ b/arch/aarch64/include/asm/cpu.h
> @@ -55,6 +55,7 @@
>  #define SCR_EL3_TME			BIT(34)
>  #define SCR_EL3_HXEn			BIT(38)
>  #define SCR_EL3_EnTP2			BIT(41)
> +#define SCR_EL3_RCWMASKEn		BIT(42)
>  #define SCR_EL3_TCR2EN			BIT(43)
>  #define SCR_EL3_SCTLR2En		BIT(44)
>  #define SCR_EL3_PIEN			BIT(45)
> @@ -92,6 +93,7 @@
>  
>  #define ID_AA64PFR1_EL1_MTE		BITS(11, 8)
>  #define ID_AA64PFR1_EL1_SME		BITS(27, 24)
> +#define ID_AA64PFR1_EL1_THE		BITS(51, 48)
>  #define ID_AA64PFR0_EL1_SVE		BITS(35, 32)
>  
>  #define ID_AA64SMFR0_EL1		s3_0_c0_c4_5
> diff --git a/arch/aarch64/init.c b/arch/aarch64/init.c
> index 5b21cb8..13a2339 100644
> --- a/arch/aarch64/init.c
> +++ b/arch/aarch64/init.c
> @@ -95,6 +95,9 @@ void cpu_init_el3(void)
>  	if (mrs_field(ID_AA64MMFR3_EL1, SCTLRX))
>  		scr |= SCR_EL3_SCTLR2En;
>  
> +	if (mrs_field(ID_AA64PFR1_EL1, THE))
> +		scr |= SCR_EL3_RCWMASKEn;
> +
>  	msr(SCR_EL3, scr);
>  
>  	msr(CPTR_EL3, cptr);
> -- 
> 2.25.1
>