[Qemu-devel] [PATCH 3/3] i386/kvm: advertise Hyper-V frequency MSRs

[Ladi Prosek]

As of kernel commit eb82feea59d6 ("KVM: hyperv: support HV_X64_MSR_TSC_FREQUENCY
and HV_X64_MSR_APIC_FREQUENCY"), KVM supports two new MSRs which are required
for nested Hyper-V to read timestamps with RDTSC + TSC page.

This commit makes QEMU advertise the MSRs with CPUID.40000003H:EAX[11] and
CPUID.40000003H:EDX[8] as specified in the Hyper-V TLFS and experimentally
verified on a Hyper-V host. The feature is enabled with the existing hv-time CPU
flag, and only if the TSC frequency is stable across migration and known.

Signed-off-by: Ladi Prosek <address@hidden>
---
 target/i386/kvm.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 77b6373..7e484a7 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -89,6 +89,7 @@ static bool has_msr_hv_vpindex;
 static bool has_msr_hv_runtime;
 static bool has_msr_hv_synic;
 static bool has_msr_hv_stimer;
+static bool has_msr_hv_frequencies;
 static bool has_msr_xss;
 
 static bool has_msr_architectural_pmu;
@@ -631,7 +632,17 @@ static int hyperv_handle_properties(CPUState *cs)
     if (cpu->hyperv_time) {
         env->features[FEAT_HYPERV_EAX] |= HV_X64_MSR_HYPERCALL_AVAILABLE;
         env->features[FEAT_HYPERV_EAX] |= HV_X64_MSR_TIME_REF_COUNT_AVAILABLE;
-        env->features[FEAT_HYPERV_EAX] |= 0x200;
+        env->features[FEAT_HYPERV_EAX] |= HV_X64_MSR_REFERENCE_TSC_AVAILABLE;
+        if (has_msr_hv_frequencies
+            /* TSC clock must be stable and known for this feature. */
+            && ((env->features[FEAT_8000_0007_EDX] & CPUID_APM_INVTSC)
+                || env->user_tsc_khz != 0)
+            && env->tsc_khz != 0) {
+
+            env->features[FEAT_HYPERV_EAX] |= HV_X64_ACCESS_FREQUENCY_MSRS;
+            env->features[FEAT_HYPERV_EDX] |=
+                HV_FEATURE_FREQUENCY_MSRS_AVAILABLE;
+        }
     }
     if (cpu->hyperv_crash && has_msr_hv_crash) {
         env->features[FEAT_HYPERV_EDX] |= HV_X64_GUEST_CRASH_MSR_AVAILABLE;
@@ -1127,6 +1138,9 @@ static int kvm_get_supported_msrs(KVMState *s)
                 case HV_X64_MSR_STIMER0_CONFIG:
                     has_msr_hv_stimer = true;
                     break;
+                case HV_X64_MSR_TSC_FREQUENCY:
+                    has_msr_hv_frequencies = true;
+                    break;
                 }
 
             }
-- 
2.9.3