qemu: cgroup: Properly set up vcpu pinning

When the default cpuset or automatic numa placement is used libvirt
would place the whole parent cgroup in the specified cpuset. This then
disallowed to re-pin the vcpus to a different cpu.

This patch pins only the vcpu threads to the default cpuset and thus
allows to re-pin them later.

The following config would fail to start:
<domain type='kvm'>
  ...
  <vcpu placement='static' cpuset='0-1' current='2'>4</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='2-3'/>
    ...

This is a regression since a39f69d2.

src/qemu/qemu_cgroup.c

@@ -645,8 +645,6 @@ static int
 qemuSetupCpusetCgroup(virDomainObjPtr vm)
 {
     qemuDomainObjPrivatePtr priv = vm->privateData;
-    char *cpu_mask = NULL;
-    int ret = -1;
 
     if (!virCgroupHasController(priv->cgroup, VIR_CGROUP_CONTROLLER_CPUSET))
         return 0;
@@ -654,25 +652,7 @@ qemuSetupCpusetCgroup(virDomainObjPtr vm)
     if (virCgroupSetCpusetMemoryMigrate(priv->cgroup, true) < 0)
         return -1;
 
-    if (vm->def->cpumask ||
-        (vm->def->placement_mode == VIR_DOMAIN_CPU_PLACEMENT_MODE_AUTO)) {
-
-        if (vm->def->placement_mode == VIR_DOMAIN_CPU_PLACEMENT_MODE_AUTO)
-            cpu_mask = virBitmapFormat(priv->autoCpuset);
-        else
-            cpu_mask = virBitmapFormat(vm->def->cpumask);
-
-        if (!cpu_mask)
-            goto cleanup;
-
-        if (virCgroupSetCpusetCpus(priv->cgroup, cpu_mask) < 0)
-            goto cleanup;
-    }
-
-    ret = 0;
- cleanup:
-    VIR_FREE(cpu_mask);
-    return ret;
+    return 0;
 }
 
 
@@ -1079,20 +1059,27 @@ qemuSetupCgroupForVcpu(virDomainObjPtr vm)
 
         /* Set vcpupin in cgroup if vcpupin xml is provided */
         if (virCgroupHasController(priv->cgroup, VIR_CGROUP_CONTROLLER_CPUSET)) {
-            /* find the right CPU to pin, otherwise
-             * qemuSetupCgroupVcpuPin will fail. */
-            for (j = 0; j < def->cputune.nvcpupin; j++) {
-                if (def->cputune.vcpupin[j]->id != i)
-                    continue;
+            virBitmapPtr cpumap = NULL;
 
-                if (qemuSetupCgroupVcpuPin(cgroup_vcpu,
-                                           def->cputune.vcpupin,
-                                           def->cputune.nvcpupin,
-                                           i) < 0)
-                    goto cleanup;
+            /* try to use the default cpu maps */
+            if (vm->def->placement_mode == VIR_DOMAIN_CPU_PLACEMENT_MODE_AUTO)
+                cpumap = priv->autoCpuset;
+            else
+                cpumap = vm->def->cpumask;
 
-                break;
+            /* lookup a more specific pinning info */
+            for (j = 0; j < def->cputune.nvcpupin; j++) {
+                if (def->cputune.vcpupin[j]->id == i) {
+                    cpumap = def->cputune.vcpupin[j]->cpumask;
+                    break;
+                }
             }
+
+            if (!cpumap)
+                continue;
+
+            if (qemuSetupCgroupEmulatorPin(cgroup_vcpu, cpumap) < 0)
+                goto cleanup;
         }
 
         virCgroupFree(&cgroup_vcpu);