[Qemu-devel] [PATCH v2 4/4] i386/kvm: advertise Hyper-V frequency MSRs

[Ladi Prosek <lprosek@redhat.com>]

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 migrations and known.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
---
 target/i386/kvm.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 2dc01c9..739334a 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;
@@ -640,7 +641,13 @@ 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_is_stable_and_known(env)) {
+            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;
@@ -1134,6 +1141,9 @@ 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