linux-kernel - [PATCH RFC 04/22] KVM: x86: hyper-v: Honor HV_MSR_TIME_REF_COUNT

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Date:   Tue, 13 Apr 2021 14:26:12 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org
Subject: [PATCH RFC 04/22] KVM: x86: hyper-v: Honor HV_MSR_TIME_REF_COUNT_AVAILABLE privilege bit

HV_X64_MSR_TIME_REF_COUNT is only available to guest when
HV_MSR_TIME_REF_COUNT_AVAILABLE bit is exposed.

Note, writing to HV_X64_MSR_TIME_REF_COUNT is unsupported so
kvm_hv_set_msr_pw() doesn't need an additional check.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/hyperv.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index b39445aabbc2..efb3d69c98fd 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1440,6 +1440,7 @@ static int kvm_hv_get_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
 	u64 data = 0;
 	struct kvm *kvm = vcpu->kvm;
 	struct kvm_hv *hv = to_kvm_hv(kvm);
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
 
 	switch (msr) {
 	case HV_X64_MSR_GUEST_OS_ID:
@@ -1449,6 +1450,10 @@ static int kvm_hv_get_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata,
 		data = hv->hv_hypercall;
 		break;
 	case HV_X64_MSR_TIME_REF_COUNT:
+		if (unlikely(!host && !(hv_vcpu->cpuid_cache.features_eax &
+					HV_MSR_TIME_REF_COUNT_AVAILABLE)))
+			return 1;
+
 		data = get_time_ref_counter(kvm);
 		break;
 	case HV_X64_MSR_REFERENCE_TSC:
-- 
2.30.2