Use configured CPU model if possible

Adds ability to provide a preferred CPU model for CPUID data decoding.
Such model would be considered as the best possible model (if it's
supported by hypervisor) regardless on number of features which have to
be added or removed for describing required CPU.

src/cpu/cpu.c

@@ -127,11 +127,13 @@ int
 cpuDecode(virCPUDefPtr cpu,
           const union cpuData *data,
           const char **models,
-          unsigned int nmodels)
+          unsigned int nmodels,
+          const char *preferred)
 {
     struct cpuArchDriver *driver;
 
-    VIR_DEBUG("cpu=%p, data=%p, nmodels=%u", cpu, data, nmodels);
+    VIR_DEBUG("cpu=%p, data=%p, nmodels=%u, preferred=%s",
+              cpu, data, nmodels, NULLSTR(preferred));
     if (models) {
         unsigned int i;
         for (i = 0; i < nmodels; i++)
@@ -160,7 +162,7 @@ cpuDecode(virCPUDefPtr cpu,
         return -1;
     }
 
-    return driver->decode(cpu, data, models, nmodels);
+    return driver->decode(cpu, data, models, nmodels, preferred);
 }
 
 

src/cpu/cpu.h

@@ -49,7 +49,8 @@ typedef int
 (*cpuArchDecode)    (virCPUDefPtr cpu,
                      const union cpuData *data,
                      const char **models,
-                     unsigned int nmodels);
+                     unsigned int nmodels,
+                     const char *preferred);
 
 typedef int
 (*cpuArchEncode)    (const virCPUDefPtr cpu,
@@ -108,7 +109,8 @@ extern int
 cpuDecode   (virCPUDefPtr cpu,
              const union cpuData *data,
              const char **models,
-             unsigned int nmodels);
+             unsigned int nmodels,
+             const char *preferred);
 
 extern int
 cpuEncode   (const char *arch,

src/cpu/cpu_x86.c

@@ -1064,7 +1064,8 @@ static int
 x86Decode(virCPUDefPtr cpu,
           const union cpuData *data,
           const char **models,
-          unsigned int nmodels)
+          unsigned int nmodels,
+          const char *preferred)
 {
     int ret = -1;
     struct x86_map *map;
@@ -1109,6 +1110,12 @@ x86Decode(virCPUDefPtr cpu,
             }
         }
 
+        if (preferred && STREQ(cpuCandidate->model, preferred)) {
+            virCPUDefFree(cpuModel);
+            cpuModel = cpuCandidate;
+            break;
+        }
+
         if (cpuModel == NULL
             || cpuModel->nfeatures > cpuCandidate->nfeatures) {
             virCPUDefFree(cpuModel);
@@ -1356,7 +1363,7 @@ x86Baseline(virCPUDefPtr *cpus,
     if (!(data = x86DataFromModel(base_model)))
         goto no_memory;
 
-    if (x86Decode(cpu, data, models, nmodels) < 0)
+    if (x86Decode(cpu, data, models, nmodels, NULL) < 0)
         goto error;
 
 cleanup:

src/qemu/qemu_conf.c

@@ -1029,7 +1029,7 @@ qemudCapsInitCPU(virCapsPtr caps,
     cpu->threads = nodeinfo.threads;
 
     if (!(data = cpuNodeData(arch))
-        || cpuDecode(cpu, data, NULL, 0) < 0)
+        || cpuDecode(cpu, data, NULL, 0, NULL) < 0)
         goto error;
 
     caps->host.cpu = cpu;
@@ -3292,6 +3292,7 @@ qemuBuildCpuArgStr(const struct qemud_driver *driver,
 
     if (ncpus > 0 && host) {
         virCPUCompareResult cmp;
+        const char *preferred;
 
         cmp = cpuGuestData(host, def->cpu, &data);
         switch (cmp) {
@@ -3309,8 +3310,13 @@ qemuBuildCpuArgStr(const struct qemud_driver *driver,
         if (VIR_ALLOC(guest) < 0 || !(guest->arch = strdup(ut->machine)))
             goto no_memory;
 
+        if (def->cpu->match == VIR_CPU_MATCH_MINIMUM)
+            preferred = host->model;
+        else
+            preferred = def->cpu->model;
+
         guest->type = VIR_CPU_TYPE_GUEST;
-        if (cpuDecode(guest, data, cpus, ncpus) < 0)
+        if (cpuDecode(guest, data, cpus, ncpus, preferred) < 0)
             goto cleanup;
 
         virBufferVSprintf(&buf, "%s", guest->model);