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

[Denis Plotnikov]

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
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