From: Roman Kagan <rkagan@virtuozzo.com>

When started in compat configuration of SynIC, e.g.

qemu-system-x86_64 -machine pc-i440fx-2.10,accel=kvm \
 -cpu host,-vmx,hv-relaxed,hv_spinlocks=0x1fff,hv-vpindex,hv-synic

or explicitly

qemu-system-x86_64 -enable-kvm -cpu host,hv-synic,x-hv-synic-kvm-only=on

QEMU crashes in hyperv_synic_reset() trying to access the non-present
qobject for SynIC.

Add the missing check for NULL.

Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reported-by: Igor Mammedov <imammedo@redhat.com>
Fixes: 9b4cf107b09d18ac30f46fd1c4de8585ccba030c
Fixes: 4a93722f9c279184e95b1e1ad775c01deec05065
Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Message-Id: <20181126152836.25379-1-rkagan@virtuozzo.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 hw/hyperv/hyperv.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/hyperv/hyperv.c b/hw/hyperv/hyperv.c
index a28e7249d8..8758635227 100644
--- a/hw/hyperv/hyperv.c
+++ b/hw/hyperv/hyperv.c
@@ -136,7 +136,11 @@ void hyperv_synic_add(CPUState *cs)
 
 void hyperv_synic_reset(CPUState *cs)
 {
-    device_reset(DEVICE(get_synic(cs)));
+    SynICState *synic = get_synic(cs);
+
+    if (synic) {
+        device_reset(DEVICE(synic));
+    }
 }
 
 static const TypeInfo synic_type_info = {
-- 
2.18.0.rc1.1.g3f1ff2140