[Devel] [PATCH] KVM: x86: add a stub for MSR_PLATFORM_INFO

[Denis Plotnikov]

On 06.06.2019 14:31, Roman Kagan wrote:
> On Thu, Jun 06, 2019 at 11:36:45AM +0300, Denis Plotnikov wrote:
>> This is done to prevent windows guest crashing while running
>> PassMark benchmark which calls rdmsr(0xce) - MSR_PLATFORM_INFO
>> from PassMark driver.
>>
>> The reason why the test driver does so is unclear, since
>> MSR_PLATFORM_INFO is used to calibrate tsc for certain Intel Atom
>> cpus (please, refer to try_msr_calibrate_tsc in arch/x86/kernel/tsc_msr.c).
>>
>> Anyway, KVM so far didn't have MSR_PLATFORM_INFO MSR implemented and
> 
> KVM has it implemented since 4.12.  Why not just backport it?
But for another purpose: "KVM: x86: virtualize cpuid faulting"
Isn't worth to backport now. Will get that functionality later while 
rebasing to newer RHEL

Denis
> 
> Roman.
> 
>> this didn't cause any problems with guest crashes on both Linux and Windows
>> platforms. So, the only reason why the crashes started now is that
>> the customer started using PassMark test on KVM platform recently.
>>
>> https://jira.sw.ru/browse/PSBM-95187
>>
>> Signed-off-by: Denis Plotnikov <dplotnikov at virtuozzo.com>
>> ---
>>   arch/x86/kvm/cpuid.h | 1 -
>>   arch/x86/kvm/x86.c   | 7 +++++++
>>   2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
>> index c4996e57d10c..fb0c6ab257cf 100644
>> --- a/arch/x86/kvm/cpuid.h
>> +++ b/arch/x86/kvm/cpuid.h
>> @@ -121,5 +121,4 @@ static inline bool guest_cpuid_is_amd(struct kvm_vcpu *vcpu)
>>   	best = kvm_find_cpuid_entry(vcpu, 0, 0);
>>   	return best && best->ebx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx;
>>   }
>> -
>>   #endif
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index f1230a251add..b855f03477f4 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -1018,6 +1018,7 @@ static u32 emulated_msrs[] = {
>>   	MSR_IA32_MCG_EXT_CTL,
>>   	MSR_IA32_SMBASE,
>>   	MSR_AMD64_VIRT_SPEC_CTRL,
>> +	MSR_PLATFORM_INFO,
>>   };
>>   
>>   static unsigned num_emulated_msrs;
>> @@ -2300,6 +2301,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>   			return 1;
>>   		vcpu->arch.osvw.status = data;
>>   		break;
>> +	case MSR_PLATFORM_INFO:
>> +		return 1;
>> +		break;
>>   	default:
>>   		if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr))
>>   			return xen_hvm_config(vcpu, data);
>> @@ -2517,6 +2521,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>   			return 1;
>>   		msr_info->data = vcpu->arch.osvw.status;
>>   		break;
>> +	case MSR_PLATFORM_INFO:
>> +		msr_info->data = 0;
>> +		break;
>>   	default:
>>   		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
>>   			return kvm_pmu_get_msr(vcpu, msr_info->index, &msr_info->data);
>> -- 
>> 2.17.0
>>

-- 
Best,
Denis