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

[Roman Kagan]

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?

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
>