KVM: hyperv: support HV_X64_MSR_TSC_FREQUENCY and HV_X64_MSR_APIC_FREQUENCY

ladipro · bonzini · commit 72c139bacfa3 · 2017-08-07T15:26:06.000+02:00
It has been experimentally confirmed that supporting these two MSRs is one
of the necessary conditions for nested Hyper-V to use the TSC page. Modern
Windows guests are noticeably slower when they fall back to reading
timestamps from the HV_X64_MSR_TIME_REF_COUNT MSR instead of using the TSC
page.

The newly supported MSRs are advertised with the AccessFrequencyRegs
partition privilege flag and CPUID.40000003H:EDX[8] "Support for
determining timer frequencies is available" (both outside of the scope of
this KVM patch).

Reviewed-by: Radim Krčmář &lt;rkrcmar@redhat.com&gt;
Signed-off-by: Ladi Prosek &lt;lprosek@redhat.com&gt;
Signed-off-by: Paolo Bonzini &lt;pbonzini@redhat.com&gt;
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
@@ -1160,6 +1160,12 @@ static int kvm_hv_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 		return stimer_get_count(vcpu_to_stimer(vcpu, timer_index),
 					pdata);
 	}
+	case HV_X64_MSR_TSC_FREQUENCY:
+		data = (u64)vcpu->arch.virtual_tsc_khz * 1000;
+		break;
+	case HV_X64_MSR_APIC_FREQUENCY:
+		data = APIC_BUS_FREQUENCY;
+		break;
 	default:
 		vcpu_unimpl(vcpu, "Hyper-V unhandled rdmsr: 0x%x\n", msr);
 		return 1;
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
@@ -54,8 +54,6 @@
 #define PRIu64 "u"
 #define PRIo64 "o"
 
-#define APIC_BUS_CYCLE_NS 1
-
 /* #define apic_debug(fmt,arg...) printk(KERN_WARNING fmt,##arg) */
 #define apic_debug(fmt, arg...)
 
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
@@ -12,6 +12,9 @@
 #define KVM_APIC_SHORT_MASK	0xc0000
 #define KVM_APIC_DEST_MASK	0x800
 
+#define APIC_BUS_CYCLE_NS       1
+#define APIC_BUS_FREQUENCY      (1000000000ULL / APIC_BUS_CYCLE_NS)
+
 struct kvm_timer {
 	struct hrtimer timer;
 	s64 period; 				/* unit: ns */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
@@ -993,6 +993,7 @@ static u32 emulated_msrs[] = {
 	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
 	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
 	HV_X64_MSR_TIME_REF_COUNT, HV_X64_MSR_REFERENCE_TSC,
+	HV_X64_MSR_TSC_FREQUENCY, HV_X64_MSR_APIC_FREQUENCY,
 	HV_X64_MSR_CRASH_P0, HV_X64_MSR_CRASH_P1, HV_X64_MSR_CRASH_P2,
 	HV_X64_MSR_CRASH_P3, HV_X64_MSR_CRASH_P4, HV_X64_MSR_CRASH_CTL,
 	HV_X64_MSR_RESET,
