target/i386: always create kvmclock device

QEMU's kvmclock device is only created when KVM PV feature bits for
kvmclock (KVM_FEATURE_CLOCKSOURCE/KVM_FEATURE_CLOCKSOURCE2) are
exposed to the guest. With 'kvm=off' cpu flag the device is not
created and we don't call KVM_GET_CLOCK/KVM_SET_CLOCK upon migration.
It was reported that without these call at least Hyper-V TSC page
clocksouce (which can be enabled independently) gets broken after
migration.

Switch to creating kvmclock QEMU device unconditionally, it seems
to always make sense to call KVM_GET_CLOCK/KVM_SET_CLOCK on migration.
Use KVM_CAP_ADJUST_CLOCK check instead of CPUID feature bits.

Reported-by: Antoine Damhet <antoine.damhet@blade-group.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200922151934.899555-1-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/kvm/clock.c

@@ -329,11 +329,14 @@ static const TypeInfo kvmclock_info = {
 };
 
 /* Note: Must be called after VCPU initialization. */
-void kvmclock_create(void)
+void kvmclock_create(bool create_always)
 {
     X86CPU *cpu = X86_CPU(first_cpu);
 
-    if (kvm_enabled() &&
+    if (!kvm_enabled() || !kvm_has_adjust_clock())
+        return;
+
+    if (create_always ||
         cpu->env.features[FEAT_KVM] & ((1ULL << KVM_FEATURE_CLOCKSOURCE) |
                                        (1ULL << KVM_FEATURE_CLOCKSOURCE2))) {
         sysbus_create_simple(TYPE_KVM_CLOCK, -1, NULL);

hw/i386/microvm.c

@@ -125,7 +125,7 @@ static void microvm_devices_init(MicrovmMachineState *mms)
 
     ioapic_init_gsi(gsi_state, "machine");
 
-    kvmclock_create();
+    kvmclock_create(true);
 
     mms->virtio_irq_base = x86_machine_is_acpi_enabled(x86ms) ? 16 : 5;
     for (i = 0; i < VIRTIO_NUM_TRANSPORTS; i++) {

hw/i386/pc.c

@@ -1657,6 +1657,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     pcmc->acpi_data_size = 0x20000 + 0x8000;
     pcmc->linuxboot_dma_enabled = true;
     pcmc->pvh_enabled = true;
+    pcmc->kvmclock_create_always = true;
     assert(!mc->get_hotplug_handler);
     mc->get_hotplug_handler = pc_get_hotplug_handler;
     mc->hotplug_allowed = pc_hotplug_allowed;

hw/i386/pc_piix.c

@@ -158,8 +158,8 @@ static void pc_init1(MachineState *machine,
 
     x86_cpus_init(x86ms, pcmc->default_cpu_version);
 
-    if (kvm_enabled() && pcmc->kvmclock_enabled) {
+    if (pcmc->kvmclock_enabled) {
-        kvmclock_create();
+        kvmclock_create(pcmc->kvmclock_create_always);
     }
 
     if (pcmc->pci_enabled) {
@@ -440,11 +440,14 @@ DEFINE_I440FX_MACHINE(v5_2, "pc-i440fx-5.2", NULL,
 
 static void pc_i440fx_5_1_machine_options(MachineClass *m)
 {
+    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
+
     pc_i440fx_5_2_machine_options(m);
     m->alias = NULL;
     m->is_default = false;
     compat_props_add(m->compat_props, hw_compat_5_1, hw_compat_5_1_len);
     compat_props_add(m->compat_props, pc_compat_5_1, pc_compat_5_1_len);
+    pcmc->kvmclock_create_always = false;
 }
 
 DEFINE_I440FX_MACHINE(v5_1, "pc-i440fx-5.1", NULL,

hw/i386/pc_q35.c

@@ -179,7 +179,7 @@ static void pc_q35_init(MachineState *machine)
 
     x86_cpus_init(x86ms, pcmc->default_cpu_version);
 
-    kvmclock_create();
+    kvmclock_create(pcmc->kvmclock_create_always);
 
     /* pci enabled */
     if (pcmc->pci_enabled) {
@@ -357,10 +357,13 @@ DEFINE_Q35_MACHINE(v5_2, "pc-q35-5.2", NULL,
 
 static void pc_q35_5_1_machine_options(MachineClass *m)
 {
+    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
+
     pc_q35_5_2_machine_options(m);
     m->alias = NULL;
     compat_props_add(m->compat_props, hw_compat_5_1, hw_compat_5_1_len);
     compat_props_add(m->compat_props, pc_compat_5_1, pc_compat_5_1_len);
+    pcmc->kvmclock_create_always = false;
 }
 
 DEFINE_Q35_MACHINE(v5_1, "pc-q35-5.1", NULL,

include/hw/i386/pc.h

@@ -118,6 +118,9 @@ struct PCMachineClass {
 
     /* use PVH to load kernels that support this feature */
     bool pvh_enabled;
+
+    /* create kvmclock device even when KVM PV features are not exposed */
+    bool kvmclock_create_always;
 };
 
 #define TYPE_PC_MACHINE "generic-pc-machine"

include/hw/kvm/clock.h

@@ -15,11 +15,11 @@
 
 #ifdef CONFIG_KVM
 
-void kvmclock_create(void);
+void kvmclock_create(bool create_always);
 
 #else /* CONFIG_KVM */
 
-static inline void kvmclock_create(void)
+static inline void kvmclock_create(bool create_always)
 {
 }
 

target/i386/kvm.c

@@ -143,6 +143,11 @@ bool kvm_has_adjust_clock_stable(void)
     return (ret == KVM_CLOCK_TSC_STABLE);
 }
 
+bool kvm_has_adjust_clock(void)
+{
+    return kvm_check_extension(kvm_state, KVM_CAP_ADJUST_CLOCK);
+}
+
 bool kvm_has_exception_payload(void)
 {
     return has_exception_payload;

target/i386/kvm_i386.h

@@ -34,6 +34,7 @@
 
 bool kvm_allows_irq0_override(void);
 bool kvm_has_smm(void);
+bool kvm_has_adjust_clock(void);
 bool kvm_has_adjust_clock_stable(void);
 bool kvm_has_exception_payload(void);
 void kvm_synchronize_all_tsc(void);