KVM: use KVM_CAP_MAX_VCPU_ID

As stated in linux/Documentation/virtual/kvm/api.txt:

The maximum possible value for max_vcpu_id can be retrieved using the
KVM_CAP_MAX_VCPU_ID of the KVM_CHECK_EXTENSION ioctl() at run-time.

If the KVM_CAP_MAX_VCPU_ID does not exist, you should assume that
max_vcpu_id is the same as the value returned from KVM_CAP_MAX_VCPUS.
Signed-off-by: NGreg Kurz <gkurz@linux.vnet.ibm.com>
Message-Id: <146424974323.5666.5471538288045048119.stgit@bahia.huguette.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

kvm-all.c

@@ -1519,10 +1519,16 @@ static int kvm_max_vcpus(KVMState *s)
     return (ret) ? ret : kvm_recommended_vcpus(s);
 }
 
+static int kvm_max_vcpu_id(KVMState *s)
+{
+    int ret = kvm_check_extension(s, KVM_CAP_MAX_VCPU_ID);
+    return (ret) ? ret : kvm_max_vcpus(s);
+}
+
 bool kvm_vcpu_id_is_valid(int vcpu_id)
 {
     KVMState *s = KVM_STATE(current_machine->accelerator);
-    return vcpu_id >= 0 && vcpu_id < kvm_max_vcpus(s);
+    return vcpu_id >= 0 && vcpu_id < kvm_max_vcpu_id(s);
 }
 
 static int kvm_init(MachineState *ms)