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

[Anshuman Khandual]

On 4/18/24 15:57, Mark Rutland wrote:
> 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.

Sure, makes sense.

> 
> Mark.
> 
>>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual at 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
>>