Re: [XEN PATCH] x86/msr: Allow hardware domain to read package C-state residency counters

[Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>]

Jan Beulich:
> On 18.07.2023 15:17, Simon Gaiser wrote:
>> --- a/xen/arch/x86/pv/emul-priv-op.c
>> +++ b/xen/arch/x86/pv/emul-priv-op.c
>> @@ -965,6 +965,20 @@ static int cf_check read_msr(
>>          *val = 0;
>>          return X86EMUL_OKAY;
>>  
>> +    case MSR_PKG_C2_RESIDENCY:
>> +    case MSR_PKG_C3_RESIDENCY:
>> +    case MSR_PKG_C6_RESIDENCY:
>> +    case MSR_PKG_C7_RESIDENCY:
>> +    case MSR_PKG_C8_RESIDENCY:
>> +    case MSR_PKG_C9_RESIDENCY:
>> +    case MSR_PKG_C10_RESIDENCY:
>> +        if ( boot_cpu_data.x86_vendor != X86_VENDOR_INTEL )
>> +            break;
>> +        if ( is_hardware_domain(currd) )
>> +            goto normal;
>> +        *val = 0;
>> +        return X86EMUL_OKAY;
> 
> In addition to what Andrew said: Why would we suddenly allow these
> reads to succeed for DomU-s?

That patch wouldn't actually allow those reads, but fake a 0 response,
or do I miss something. If you mean that behavior: I just mirrored what
is done there in some of the other cases. If you prefer something else,
for example treating it as unimplemented, I can change that.

Simon

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