Re: [bootwrapper PATCH 1/2] aarch64: Disable trapping into EL3 while accessing MDSELR_EL1

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

On Thu, Apr 04, 2024 at 01:07:25PM +0530, Anshuman Khandual wrote:
> This disables trapping into EL3 while accessing MDSELR_EL1 either in EL1 or
> EL2 via setting MDCR_EL3.EBWE. But first ensure that FEAT_Debugv8p9 feature
> is implemented and enabled looking into ID_AA64DFR0_EL1.

The patch itself looks fine, but I'm going to reword the commit message for clarity:

| aarch64: Enable access to MDSELR_EL1 from EL2 and below
| 
| FEAT_Debugv8p9 adds a new MDSELR_EL1 register to select between banks of
| breakpoints and watchpoints. Accesses to MDSELR_EL1 from EL2 and below trap
| to EL3 unless MDCR_EL3.EBWE is set.
| 
| Enable access to MDSELR_EL1 when it is implemented.

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 d1f8fd9..124ef91 100644
> --- a/arch/aarch64/include/asm/cpu.h
> +++ b/arch/aarch64/include/asm/cpu.h
> @@ -41,6 +41,7 @@
>  #define MDCR_EL3_NSTB_NS_NOTRAP			(UL(3) << 24)
>  #define MDCR_EL3_SBRBE_NOTRAP_NOPROHIBIT	(UL(3) << 32)
>  #define MDCR_EL3_ENPMSN				BIT(36)
> +#define MDCR_EL3_EBWE				BIT(43)
>  
>  #define SCR_EL3_RES1			BITS(5, 4)
>  #define SCR_EL3_NS			BIT(0)
> @@ -62,6 +63,7 @@
>  #define ID_AA64DFR0_EL1_PMSVER		BITS(35, 32)
>  #define ID_AA64DFR0_EL1_TRACEBUFFER	BITS(47, 44)
>  #define ID_AA64DFR0_EL1_BRBE		BITS(55, 52)
> +#define ID_AA64DFR0_EL1_DEBUGVER	BITS(3, 0)
>  
>  #define ID_AA64ISAR0_EL1_TME		BITS(27, 24)
>  
> diff --git a/arch/aarch64/init.c b/arch/aarch64/init.c
> index c4e91e4..37cb45f 100644
> --- a/arch/aarch64/init.c
> +++ b/arch/aarch64/init.c
> @@ -105,6 +105,9 @@ void cpu_init_el3(void)
>  	if (mrs_field(ID_AA64DFR0_EL1, BRBE))
>  		mdcr |= MDCR_EL3_SBRBE_NOTRAP_NOPROHIBIT;
>  
> +	if (mrs_field(ID_AA64DFR0_EL1, DEBUGVER) >= 11)
> +		mdcr |= MDCR_EL3_EBWE;
> +
>  	msr(MDCR_EL3, mdcr);
>  
>  	if (mrs_field(ID_AA64PFR0_EL1, SVE)) {
> -- 
> 2.25.1
> 

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