cpu: Avoid adding <vendor> to custom CPUs

Guest CPU definitions with mode='custom' and missing <vendor> are
expected to run on a host CPU from any vendor as long as the required
CPU model can be used as a guest CPU on the host. But even though no CPU
vendor was explicitly requested we would sometimes force it due to a bug
in virCPUUpdate and virCPUTranslate.

The bug would effectively forbid cross vendor migrations even if they
were previously working just fine.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

src/conf/cpu_conf.c

@@ -132,20 +132,42 @@ virCPUDefCopyModelFilter(virCPUDefPtr dst,
 }
 
 
+/**
+ * virCPUDefStealModel:
+ *
+ * Move CPU model related parts virCPUDef from @src to @dst. If @keepVendor
+ * is true, the function keeps the original vendor/vendor_id in @dst rather
+ * than overwriting it with the values from @src.
+ */
 void
 virCPUDefStealModel(virCPUDefPtr dst,
-                    virCPUDefPtr src)
+                    virCPUDefPtr src,
+                    bool keepVendor)
 {
+    char *vendor;
+    char *vendor_id;
+
+    if (keepVendor) {
+        VIR_STEAL_PTR(vendor, dst->vendor);
+        VIR_STEAL_PTR(vendor_id, dst->vendor_id);
+    }
+
     virCPUDefFreeModel(dst);
 
     VIR_STEAL_PTR(dst->model, src->model);
-    VIR_STEAL_PTR(dst->vendor, src->vendor);
-    VIR_STEAL_PTR(dst->vendor_id, src->vendor_id);
     VIR_STEAL_PTR(dst->features, src->features);
     dst->nfeatures_max = src->nfeatures_max;
     src->nfeatures_max = 0;
     dst->nfeatures = src->nfeatures;
     src->nfeatures = 0;
+
+    if (keepVendor) {
+        dst->vendor = vendor;
+        dst->vendor_id = vendor_id;
+    } else {
+        VIR_STEAL_PTR(dst->vendor, src->vendor);
+        VIR_STEAL_PTR(dst->vendor_id, src->vendor_id);
+    }
 }
 
 

src/conf/cpu_conf.h

@@ -139,7 +139,8 @@ virCPUDefCopyModelFilter(virCPUDefPtr dst,
 
 void
 virCPUDefStealModel(virCPUDefPtr dst,
-                    virCPUDefPtr src);
+                    virCPUDefPtr src,
+                    bool keepVendor);
 
 virCPUDefPtr
 virCPUDefCopy(const virCPUDef *cpu);

src/cpu/cpu_arm.c

@@ -67,7 +67,7 @@ virCPUarmUpdate(virCPUDefPtr guest,
     if (virCPUDefCopyModel(updated, host, true) < 0)
         goto cleanup;
 
-    virCPUDefStealModel(guest, updated);
+    virCPUDefStealModel(guest, updated, false);
     guest->mode = VIR_CPU_MODE_CUSTOM;
     guest->match = VIR_CPU_MATCH_EXACT;
     ret = 0;

src/cpu/cpu_x86.c

@@ -2576,7 +2576,8 @@ x86UpdateHostModel(virCPUDefPtr guest,
             goto cleanup;
     }
 
-    virCPUDefStealModel(guest, updated);
+    virCPUDefStealModel(guest, updated,
+                        guest->mode == VIR_CPU_MODE_CUSTOM);
     guest->mode = VIR_CPU_MODE_CUSTOM;
     guest->match = VIR_CPU_MATCH_EXACT;
     ret = 0;
@@ -2737,7 +2738,7 @@ virCPUx86Translate(virCPUDefPtr cpu,
             goto cleanup;
     }
 
-    virCPUDefStealModel(cpu, translated);
+    virCPUDefStealModel(cpu, translated, true);
     ret = 0;
 
  cleanup:

tests/cputestdata/x86-host+guest,model486-result.xml

 <cpu mode='custom' match='exact'>
   <model fallback='allow'>486</model>
-  <vendor>Intel</vendor>
   <topology sockets='2' cores='4' threads='1'/>
   <feature policy='require' name='de'/>
   <feature policy='require' name='tsc'/>

tests/cputestdata/x86-host+guest,models-result.xml

 <cpu mode='custom' match='exact'>
   <model fallback='allow'>Nehalem</model>
-  <vendor>Intel</vendor>
   <topology sockets='2' cores='4' threads='1'/>
   <feature policy='force' name='pbe'/>
   <feature policy='force' name='monitor'/>

tests/cputestdata/x86-host+min.xml

 <cpu mode='custom' match='exact'>
   <model fallback='allow'>Penryn</model>
-  <vendor>Intel</vendor>
   <feature policy='require' name='dca'/>
   <feature policy='require' name='xtpr'/>
   <feature policy='require' name='tm2'/>

tests/cputestdata/x86-host+pentium3.xml

 <cpu mode='custom' match='exact'>
   <model fallback='allow'>Penryn</model>
-  <vendor>Intel</vendor>
   <feature policy='require' name='dca'/>
   <feature policy='require' name='xtpr'/>
   <feature policy='require' name='tm2'/>

tests/cputestdata/x86-host-Haswell-noTSX+Haswell-noTSX,haswell-result.xml

 <cpu mode='custom' match='exact'>
   <model fallback='allow'>Haswell</model>
-  <vendor>Intel</vendor>
   <topology sockets='1' cores='2' threads='2'/>
   <feature policy='disable' name='hle'/>
   <feature policy='disable' name='rtm'/>

tests/cputestdata/x86-host-better+pentium3-result.xml

 <cpu mode='custom' match='exact'>
   <model fallback='allow'>Nehalem</model>
-  <vendor>Intel</vendor>
   <feature policy='require' name='dca'/>
   <feature policy='require' name='xtpr'/>
   <feature policy='require' name='tm2'/>