Re: [boot-wrapper 1/3] aarch64: Enable access into 128 bit system registers from EL2 and below

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 7/25/24 14:14, Mark Rutland wrote:
> On Tue, Jul 23, 2024 at 04:36:28PM +0530, Anshuman Khandual wrote:
>> FEAT_D128 adds 128 bit system registers like PAR_EL1, TTBR0_EL1, TTBR1_EL1,
>> TTBR0_EL2, TTBR1_EL2, TTBR0_EL12, TTBR1_EL12 , VTTBR_EL2, RCWMASK_EL1, and
>> RCWSMASK_EL1. But access into these register from EL2 and below trap to EL3
>> unless SCR_EL3.D128En is set.
> 
> Do we need to initialize any of these new bits, or do they have no
> effect on a lower EL unless explicitly opted-in at that lower EL?

Unlike SCTRL2_EL1/EL2, these are actual end use registers for the lower
EL and only available in 128 bit width format when FEAT_D128 is both
implemented and opted in.

> 
> Otherwise this looks superficially fine, but it should come after
> enabling SCTLR2.

Sure, will moved it after SCTLR2 patch.

> 
> Mark.
> 
>>
>> Enable access to 128 bit registers when they are implemented.
>>
>> 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 124ef91..0b8b463 100644
>> --- a/arch/aarch64/include/asm/cpu.h
>> +++ b/arch/aarch64/include/asm/cpu.h
>> @@ -57,6 +57,7 @@
>>  #define SCR_EL3_EnTP2			BIT(41)
>>  #define SCR_EL3_TCR2EN			BIT(43)
>>  #define SCR_EL3_PIEN			BIT(45)
>> +#define SCR_EL3_D128En			BIT(47)
>>  
>>  #define HCR_EL2_RES1			BIT(1)
>>  
>> @@ -85,6 +86,7 @@
>>  #define ID_AA64MMFR3_EL1_S2PIE		BITS(15, 12)
>>  #define ID_AA64MMFR3_EL1_S1POE		BITS(19, 16)
>>  #define ID_AA64MMFR3_EL1_S2POE		BITS(23, 20)
>> +#define ID_AA64MMFR3_EL1_D128		BITS(35, 32)
>>  
>>  #define ID_AA64PFR1_EL1_MTE		BITS(11, 8)
>>  #define ID_AA64PFR1_EL1_SME		BITS(27, 24)
>> diff --git a/arch/aarch64/init.c b/arch/aarch64/init.c
>> index 37cb45f..7d9d0d9 100644
>> --- a/arch/aarch64/init.c
>> +++ b/arch/aarch64/init.c
>> @@ -89,6 +89,9 @@ void cpu_init_el3(void)
>>  	if (!kernel_is_32bit())
>>  		scr |= SCR_EL3_RW;
>>  
>> +	if (mrs_field(ID_AA64MMFR3_EL1, D128))
>> +		scr |= SCR_EL3_D128En;
>> +
>>  	msr(SCR_EL3, scr);
>>  
>>  	msr(CPTR_EL3, cptr);
>> -- 
>> 2.25.1
>>