Most machines don't allow sysbus devices like "kvmclock" to be
created from the command-line, but some of them do (the ones with
has_dynamic_sysbus=true). In those cases, it's possible to
manually create a kvmclock device without KVM being enabled,
making QEMU crash:

  $ qemu-system-x86_64 -machine q35,accel=tcg -device kvmclock
  Segmentation fault (core dumped)

This changes kvmclock's realize method to return an error if KVM
is disabled, to ensure it won't crash QEMU.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 hw/i386/kvm/clock.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c
index ef9d560f9c..13eca374cd 100644
--- a/hw/i386/kvm/clock.c
+++ b/hw/i386/kvm/clock.c
@@ -22,6 +22,7 @@
 #include "kvm_i386.h"
 #include "hw/sysbus.h"
 #include "hw/kvm/clock.h"
+#include "qapi/error.h"
 
 #include <linux/kvm.h>
 #include <linux/kvm_para.h>
@@ -208,6 +209,11 @@ static void kvmclock_realize(DeviceState *dev, Error **errp)
 {
     KVMClockState *s = KVM_CLOCK(dev);
 
+    if (!kvm_enabled()) {
+        error_setg(errp, "kvmclock device requires KVM");
+        return;
+    }
+
     kvm_update_clock(s);
 
     qemu_add_vm_change_state_handler(kvmclock_vm_state_change, s);
-- 
2.11.0.259.g40922b1