qemu: Error out if setting vcpu count would lead to invalid config

When the domain definition describes a machine with NUMA, setting the
maximum vCPU count via the API might lead to an invalid config.

Add a check that will forbid this until we add more advanced cpu config
capabilities.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1327499

src/libvirt_private.syms

@@ -674,6 +674,7 @@ virNodeDeviceObjUnlock;
 virDomainNumaCheckABIStability;
 virDomainNumaEquals;
 virDomainNumaFree;
+virDomainNumaGetCPUCountTotal;
 virDomainNumaGetMaxCPUID;
 virDomainNumaGetMemorySize;
 virDomainNumaGetNodeCount;

src/qemu/qemu_driver.c

@@ -4903,6 +4903,13 @@ qemuDomainSetVcpusFlags(virDomainPtr dom, unsigned int nvcpus,
 
     if (persistentDef) {
         if (flags & VIR_DOMAIN_VCPU_MAXIMUM) {
+            if (virDomainNumaGetCPUCountTotal(persistentDef->numa) > nvcpus) {
+                virReportError(VIR_ERR_INVALID_ARG, "%s",
+                               _("Number of CPUs in <numa> exceeds the desired "
+                                 "maximum vcpu count"));
+                goto endjob;
+            }
+
             if (virDomainDefSetVcpusMax(persistentDef, nvcpus) < 0)
                 goto endjob;
         } else {