pc: kvm: check if KVM has free memory slots to avoid abort()

When more memory devices are used than available
KVM memory slots, QEMU crashes with:

kvm_alloc_slot: no free slot available
Aborted (core dumped)

Fix this by checking that KVM has a free slot before
attempting to map memory in guest address space.
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/i386/pc.c

@@ -1598,6 +1598,11 @@ static void pc_dimm_plug(HotplugHandler *hotplug_dev,
         goto out;
     }
 
+    if (kvm_enabled() && !kvm_has_free_slot(machine)) {
+        error_setg(&local_err, "hypervisor has no free memory slots left");
+        goto out;
+    }
+
     memory_region_add_subregion(&pcms->hotplug_memory,
                                 addr - pcms->hotplug_memory_base, mr);
     vmstate_register_ram(mr, dev);

include/sysemu/kvm.h

@@ -163,6 +163,7 @@ extern KVMState *kvm_state;
 
 /* external API */
 
+bool kvm_has_free_slot(MachineState *ms);
 int kvm_has_sync_mmu(void);
 int kvm_has_vcpu_events(void);
 int kvm_has_robust_singlestep(void);

kvm-all.c

@@ -132,7 +132,7 @@ static const KVMCapabilityInfo kvm_required_capabilites[] = {
     KVM_CAP_LAST_INFO
 };
 
-static KVMSlot *kvm_alloc_slot(KVMState *s)
+static KVMSlot *kvm_get_free_slot(KVMState *s)
 {
     int i;
 
@@ -142,6 +142,22 @@ static KVMSlot *kvm_alloc_slot(KVMState *s)
         }
     }
 
+    return NULL;
+}
+
+bool kvm_has_free_slot(MachineState *ms)
+{
+    return kvm_get_free_slot(KVM_STATE(ms->accelerator));
+}
+
+static KVMSlot *kvm_alloc_slot(KVMState *s)
+{
+    KVMSlot *slot = kvm_get_free_slot(s);
+
+    if (slot) {
+        return slot;
+    }
+
     fprintf(stderr, "%s: no free slot available\n", __func__);
     abort();
 }

kvm-stub.c

@@ -147,4 +147,9 @@ int kvm_irqchip_remove_irqfd_notifier(KVMState *s, EventNotifier *n, int virq)
 {
     return -ENOSYS;
 }
+
+bool kvm_has_free_slot(MachineState *ms)
+{
+    return false;
+}
 #endif