Re: [RFC PATCH 4/5] target/arm: enable feature ARM_FEATURE_EL2 if EL2 is supported

[Miguel Luis]

Hi Richard,

> On 27 Feb 2023, at 18:24, Richard Henderson <richard.henderson@linaro.org> 
> wrote:
> 
> On 2/27/23 06:37, Miguel Luis wrote:
>> From: Haibo Xu <haibo.xu@linaro.org>
>> KVM_CAP_ARM_EL2 must be supported by the cpu to enable ARM_FEATURE_EL2.
>> EL2 bits on ID_AA64PFR0 state unsupported on the value 0b0000.
>> Ref: 
>> https://lore.kernel.org/qemu-devel/b7c2626e6c720ccc43e57197dff3dac72d613640.1616052890.git.haibo.xu@linaro.org/
>> Signed-off-by: Haibo Xu <haibo.xu@linaro.org>
>> [Miguel Luis: use of ID_AA64PFR0 for cpu features]
>> Signed-off-by: Miguel Luis <miguel.luis@oracle.com>
>> ---
>>  target/arm/cpu.h   |  2 +-
>>  target/arm/kvm64.c | 16 ++++++++++++++++
>>  2 files changed, 17 insertions(+), 1 deletion(-)
>> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
>> index 9aeed3c848..de2a88b43e 100644
>> --- a/target/arm/cpu.h
>> +++ b/target/arm/cpu.h
>> @@ -3961,7 +3961,7 @@ static inline bool isar_feature_aa64_aa32_el1(const 
>> ARMISARegisters *id)
>>    static inline bool isar_feature_aa64_aa32_el2(const ARMISARegisters *id)
>>  {
>> -    return FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, EL2) >= 2;
>> +    return FIELD_EX64(id->id_aa64pfr0, ID_AA64PFR0, EL2) != 0;
>>  }
> 
> No, this predicate is testing if EL2 supports AArch32 more.
> 
>> @@ -714,6 +723,10 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures 
>> *ahcf)
>>      features |= 1ULL << ARM_FEATURE_PMU;
>>      features |= 1ULL << ARM_FEATURE_GENERIC_TIMER;
>>  +    if (el2_supported) {
>> +        features |= 1ULL << ARM_FEATURE_EL2;
>> +    }
> 
> This is the test you want...
> 
>> @@ -881,6 +894,9 @@ int kvm_arch_init_vcpu(CPUState *cs)
>>          assert(kvm_arm_sve_supported());
>>          cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_SVE;
>>      }
>> +    if (cpu_isar_feature(aa64_aa32_el2, cpu)) {
>> +        cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_HAS_EL2;
>> +    }
> 
> ... here.
> 
> While you could add a new isar_feature predicate for EL2 supported in AArch64 
> mode, the feature test is equivalent and good enough, and is more obviously 
> tied to the required KVM support.
> 
> 

Thank you for the explanation. I will take it into consideration on the next 
version.

Miguel

> r~