KVM: VMX: Use a scaled host TSC for guest readings of MSR_IA32_TSC

This patch makes kvm-intel to return a scaled host TSC plus the TSC
offset when handling guest readings to MSR_IA32_TSC.

Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 890295287afa..c6016e4a5af0 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2371,15 +2371,16 @@ static void setup_msrs(struct vcpu_vmx *vmx)
 
 /*
  * reads and returns guest's timestamp counter "register"
- * guest_tsc = host_tsc + tsc_offset    -- 21.3
+ * guest_tsc = (host_tsc * tsc multiplier) >> 48 + tsc_offset
+ * -- Intel TSC Scaling for Virtualization White Paper, sec 1.3
  */
-static u64 guest_read_tsc(void)
+static u64 guest_read_tsc(struct kvm_vcpu *vcpu)
 {
         u64 host_tsc, tsc_offset;
 
         host_tsc = rdtsc();
         tsc_offset = vmcs_read64(TSC_OFFSET);
-        return host_tsc + tsc_offset;
+        return kvm_scale_tsc(vcpu, host_tsc) + tsc_offset;
 }
 
 /*
@@ -2771,7 +2772,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
         case MSR_EFER:
                 return kvm_get_msr_common(vcpu, msr_info);
         case MSR_IA32_TSC:
-                msr_info->data = guest_read_tsc();
+                msr_info->data = guest_read_tsc(vcpu);
                 break;
         case MSR_IA32_SYSENTER_CS:
                 msr_info->data = vmcs_read32(GUEST_SYSENTER_CS);