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

[Roman Kagan]

On Thu, Jun 06, 2019 at 03:11:10PM +0300, Denis Plotnikov wrote:
> 
> 
> 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

Doesn't it apply cleanly?  The rebase is easier if you don't need to
modify the patch.

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