cpu: Move check for NULL CPU model inside the driver

While the check is appropriate for eg. the x86 and generic drivers,
there are some valid ppc64 guest configurations where the CPU
model is supposed to be NULL.

Moving this check from the generic code to the drivers makes it
possible to accomodate both use cases.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1251927

src/cpu/cpu.c

@@ -142,12 +142,6 @@ cpuCompare(virCPUDefPtr host,
 
     VIR_DEBUG("host=%p, cpu=%p", host, cpu);
 
-    if (!cpu->model) {
-        virReportError(VIR_ERR_INVALID_ARG, "%s",
-                       _("no guest CPU model specified"));
-        return VIR_CPU_COMPARE_ERROR;
-    }
-
     if ((driver = cpuGetSubDriver(host->arch)) == NULL)
         return VIR_CPU_COMPARE_ERROR;
 
@@ -376,12 +370,6 @@ cpuGuestData(virCPUDefPtr host,
 
     VIR_DEBUG("host=%p, guest=%p, data=%p, msg=%p", host, guest, data, msg);
 
-    if (!guest->model) {
-        virReportError(VIR_ERR_INVALID_ARG, "%s",
-                       _("no guest CPU model specified"));
-        return VIR_CPU_COMPARE_ERROR;
-    }
-
     if ((driver = cpuGetSubDriver(host->arch)) == NULL)
         return VIR_CPU_COMPARE_ERROR;
 

src/cpu/cpu_generic.c

@@ -65,6 +65,12 @@ genericCompare(virCPUDefPtr host,
     size_t i;
     unsigned int reqfeatures;
 
+    if (!cpu->model) {
+        virReportError(VIR_ERR_INVALID_ARG, "%s",
+                       _("no guest CPU model specified"));
+        goto cleanup;
+    }
+
     if ((cpu->arch != VIR_ARCH_NONE &&
          host->arch != cpu->arch) ||
         STRNEQ(host->model, cpu->model)) {

src/cpu/cpu_ppc64.c

@@ -71,7 +71,8 @@ ppc64ConvertLegacyCPUDef(const virCPUDef *legacy)
     if (!(cpu = virCPUDefCopy(legacy)))
         goto out;
 
-    if (!(STREQ(cpu->model, "POWER7_v2.1") ||
+    if (!cpu->model ||
+        !(STREQ(cpu->model, "POWER7_v2.1") ||
           STREQ(cpu->model, "POWER7_v2.3") ||
           STREQ(cpu->model, "POWER7+_v2.1") ||
           STREQ(cpu->model, "POWER8_v1.0"))) {

src/cpu/cpu_x86.c

@@ -1371,6 +1371,12 @@ x86Compute(virCPUDefPtr host,
     virArch arch;
     size_t i;
 
+    if (!cpu->model) {
+        virReportError(VIR_ERR_INVALID_ARG, "%s",
+                       _("no guest CPU model specified"));
+        return VIR_CPU_COMPARE_ERROR;
+    }
+
     if (cpu->arch != VIR_ARCH_NONE) {
         bool found = false;