[PATCH v2 2/2] i386: provide simple 'hyperv=on' option to x86 machine types

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Enabling Hyper-V emulation for a Windows VM is a tiring experience as it
requires listing all currently supported enlightenments ("hv_*" CPU
features) explicitly. We do have a 'hv_passthrough' mode enabling
everything but it can't be used in production as it prevents migration.

Introduce a simple 'hyperv=on' option for all x86 machine types enabling
all currently supported Hyper-V enlightenments. Later, when new
enlightenments get implemented, we will be adding them to newer machine
types only (by disabling them for legacy machine types) thus preserving
migration.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 docs/hyperv.txt       |  8 ++++++++
 hw/i386/x86.c         | 42 ++++++++++++++++++++++++++++++++++++++++++
 include/hw/i386/x86.h |  7 +++++++
 3 files changed, 57 insertions(+)

diff --git a/docs/hyperv.txt b/docs/hyperv.txt
index 5df00da54fc4..1a76a07f8417 100644
--- a/docs/hyperv.txt
+++ b/docs/hyperv.txt
@@ -29,6 +29,14 @@ When any set of the Hyper-V enlightenments is enabled, QEMU changes hypervisor
 identification (CPUID 0x40000000..0x4000000A) to Hyper-V. KVM identification
 and features are kept in leaves 0x40000100..0x40000101.
 
+Hyper-V enlightenments can be enabled in bulk by specifying 'hyperv=on' to an
+x86 machine type:
+
+  qemu-system-x86_64 -machine q35,accel=kvm,kernel-irqchip=split,hyperv=on ...
+
+Note, new enlightenments are only added to the latest (in-develompent) machine
+type, older machine types keep the list of the supported features intact to
+safeguard migration.
 
 3. Existing enlightenments
 ===========================
diff --git a/hw/i386/x86.c b/hw/i386/x86.c
index 49e1d419b2ce..7a8e0313aedb 100644
--- a/hw/i386/x86.c
+++ b/hw/i386/x86.c
@@ -418,6 +418,18 @@ void x86_cpu_pre_plug(HotplugHandler *hotplug_dev,
     cs->cpu_index = idx;
 
     numa_cpu_pre_plug(cpu_slot, dev, errp);
+
+    if (x86ms->hyperv_enabled) {
+        X86MachineClass *x86mc = X86_MACHINE_GET_CLASS(x86ms);
+        uint64_t hyperv_features = x86mc->default_hyperv_features;
+
+        /* Enlightened VMCS is only available on Intel/VMX */
+        if (!kvm_hv_evmcs_available()) {
+            hyperv_features &= ~BIT(HYPERV_FEAT_EVMCS);
+        }
+
+        cpu->hyperv_features |= hyperv_features;
+    }
 }
 
 CpuInstanceProperties
@@ -1199,6 +1211,20 @@ static void x86_machine_set_acpi(Object *obj, Visitor *v, const char *name,
     visit_type_OnOffAuto(v, name, &x86ms->acpi, errp);
 }
 
+static bool x86_machine_get_hyperv(Object *obj, Error **errp)
+{
+    X86MachineState *x86ms = X86_MACHINE(obj);
+
+    return x86ms->hyperv_enabled;
+}
+
+static void x86_machine_set_hyperv(Object *obj, bool value, Error **errp)
+{
+    X86MachineState *x86ms = X86_MACHINE(obj);
+
+    x86ms->hyperv_enabled = value;
+}
+
 static void x86_machine_initfn(Object *obj)
 {
     X86MachineState *x86ms = X86_MACHINE(obj);
@@ -1222,6 +1248,16 @@ static void x86_machine_class_init(ObjectClass *oc, void *data)
     x86mc->save_tsc_khz = true;
     nc->nmi_monitor_handler = x86_nmi;
 
+    /* Hyper-V features enabled with 'hyperv=on' */
+    x86mc->default_hyperv_features = BIT(HYPERV_FEAT_RELAXED) |
+        BIT(HYPERV_FEAT_VAPIC) | BIT(HYPERV_FEAT_TIME) |
+        BIT(HYPERV_FEAT_CRASH) | BIT(HYPERV_FEAT_RESET) |
+        BIT(HYPERV_FEAT_VPINDEX) | BIT(HYPERV_FEAT_RUNTIME) |
+        BIT(HYPERV_FEAT_SYNIC) | BIT(HYPERV_FEAT_STIMER) |
+        BIT(HYPERV_FEAT_FREQUENCIES) | BIT(HYPERV_FEAT_REENLIGHTENMENT) |
+        BIT(HYPERV_FEAT_TLBFLUSH) | BIT(HYPERV_FEAT_EVMCS) |
+        BIT(HYPERV_FEAT_IPI) | BIT(HYPERV_FEAT_STIMER_DIRECT);
+
     object_class_property_add(oc, X86_MACHINE_SMM, "OnOffAuto",
         x86_machine_get_smm, x86_machine_set_smm,
         NULL, NULL);
@@ -1233,6 +1269,12 @@ static void x86_machine_class_init(ObjectClass *oc, void *data)
         NULL, NULL);
     object_class_property_set_description(oc, X86_MACHINE_ACPI,
         "Enable ACPI");
+
+    object_class_property_add_bool(oc, X86_MACHINE_HYPERV,
+        x86_machine_get_hyperv, x86_machine_set_hyperv);
+
+    object_class_property_set_description(oc, X86_MACHINE_HYPERV,
+        "Enable Hyper-V enlightenments");
 }
 
 static const TypeInfo x86_machine_info = {
diff --git a/include/hw/i386/x86.h b/include/hw/i386/x86.h
index 56080bd1fb14..c6e9c8500357 100644
--- a/include/hw/i386/x86.h
+++ b/include/hw/i386/x86.h
@@ -38,6 +38,9 @@ struct X86MachineClass {
     bool save_tsc_khz;
     /* Enables contiguous-apic-ID mode */
     bool compat_apic_id_mode;
+
+    /* Hyper-V features enabled with 'hyperv=on' */
+    uint64_t default_hyperv_features;
 };
 
 struct X86MachineState {
@@ -72,10 +75,14 @@ struct X86MachineState {
      * will be translated to MSI messages in the address space.
      */
     AddressSpace *ioapic_as;
+
+    /* Hyper-V emulation */
+    bool hyperv_enabled;
 };
 
 #define X86_MACHINE_SMM              "smm"
 #define X86_MACHINE_ACPI             "acpi"
+#define X86_MACHINE_HYPERV           "hyperv"
 
 #define TYPE_X86_MACHINE   MACHINE_TYPE_NAME("x86")
 OBJECT_DECLARE_TYPE(X86MachineState, X86MachineClass, X86_MACHINE)
-- 
2.29.2