When Hyper-V SynIC is enabled, we may need to allow Windows guests to make
hypercalls (POST_MESSAGES/SIGNAL_EVENTS). No issue is currently observed
because KVM is very permissive, allowing these hypercalls regarding of
guest visible CPUid bits.
Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
---
target/i386/kvm/hyperv-proto.h | 6 ++++++
target/i386/kvm/kvm.c | 6 ++++++
2 files changed, 12 insertions(+)
diff --git a/target/i386/kvm/hyperv-proto.h b/target/i386/kvm/hyperv-proto.h
index e30d64b4ade4..5fbb385cc136 100644
--- a/target/i386/kvm/hyperv-proto.h
+++ b/target/i386/kvm/hyperv-proto.h
@@ -38,6 +38,12 @@
#define HV_ACCESS_FREQUENCY_MSRS (1u << 11)
#define HV_ACCESS_REENLIGHTENMENTS_CONTROL (1u << 13)
+/*
+ * HV_CPUID_FEATURES.EBX bits
+ */
+#define HV_POST_MESSAGES (1u << 4)
+#define HV_SIGNAL_EVENTS (1u << 5)
+
/*
* HV_CPUID_FEATURES.EDX bits
*/
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index a3897d4d8788..6a32d43e6ec1 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -1343,6 +1343,12 @@ static int hyperv_fill_cpuids(CPUState *cs,
/* Unconditionally required with any Hyper-V enlightenment */
c->eax |= HV_HYPERCALL_AVAILABLE;
+ /* SynIC and Vmbus devices require messages/signals hypercalls */
+ if (hyperv_feat_enabled(cpu, HYPERV_FEAT_SYNIC) &&
+ !cpu->hyperv_synic_kvm_only) {
+ c->ebx |= HV_POST_MESSAGES | HV_SIGNAL_EVENTS;
+ }
+
/* Not exposed by KVM but needed to make CPU hotplug in Windows work */
c->edx |= HV_CPU_DYNAMIC_PARTITIONING_AVAILABLE;
--
2.31.1
