Re: [PATCH 1/2] target/arm: Add cpu property to control pauth

[Richard Henderson]

On 8/12/20 4:00 AM, Andrew Jones wrote:
> On Tue, Aug 11, 2020 at 11:53:38PM -0700, Richard Henderson wrote:
>> The crypto overhead of emulating pauth can be significant for
>> some workloads.  Add an enumeration property that allows the
>> feature to be turned off, on with the architected algorithm,
>> or on with an implementation defined algorithm.
>>
>> The architected algorithm is quite expensive to emulate;
>> using another algorithm may allow hardware acceleration.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>  target/arm/cpu64.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 64 insertions(+)
>>
>> diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
>> index dd696183df..3181d0e2f8 100644
>> --- a/target/arm/cpu64.c
>> +++ b/target/arm/cpu64.c
>> @@ -572,6 +572,69 @@ void aarch64_add_sve_properties(Object *obj)
>>      }
>>  }
>>  
>> +static const char * const pauth_names[] = {
>> +    "off", "impdef", "arch"
>> +};
> 
> Hi Richard,
> 
> Please add three boolean properties, rather than one enum:
> 
> pauth:            enable support of the pauth feature
> pauth-fast:       enable QEMU's fast non-cryptographic hash for pauth
>                   (pauth must be enabled)
> pauth-arch:       enable the architected algorithm for pauth
>                   (pauth must be enabled)
> 
> These booleans can then be added to the cpu feature probing list used by
> qmp_query_cpu_model_expansion()

Why are 3 booleans better than one enum?

I'd forgotten about qmp_query_cpu_model_expansion(); can it not take anything
but booleans?


r~