[PATCH] target/i386: always create kvmclock device

[Vitaly Kuznetsov <vkuznets@redhat.com>]

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>
---
 hw/i386/kvm/clock.c    | 6 +-----
 target/i386/kvm.c      | 5 +++++
 target/i386/kvm_i386.h | 1 +
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c
index 64283358f91d..526c9ea5172b 100644
--- a/hw/i386/kvm/clock.c
+++ b/hw/i386/kvm/clock.c
@@ -330,11 +330,7 @@ static const TypeInfo kvmclock_info = {
 /* Note: Must be called after VCPU initialization. */
 void kvmclock_create(void)
 {
-    X86CPU *cpu = X86_CPU(first_cpu);
-
-    if (kvm_enabled() &&
-        cpu->env.features[FEAT_KVM] & ((1ULL << KVM_FEATURE_CLOCKSOURCE) |
-                                       (1ULL << KVM_FEATURE_CLOCKSOURCE2))) {
+    if (kvm_enabled() && kvm_has_adjust_clock()) {
         sysbus_create_simple(TYPE_KVM_CLOCK, -1, NULL);
     }
 }
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 4a8b3a41c1bc..20b31b65307b 100644
--- a/target/i386/kvm.c
+++ b/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;
diff --git a/target/i386/kvm_i386.h b/target/i386/kvm_i386.h
index 064b8798a26c..0fce4e51d2d6 100644
--- a/target/i386/kvm_i386.h
+++ b/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);
-- 
2.25.4