qemu: Fix GIC behavior for the default case

When no GIC version is specified, we currently default to GIC v2;
however, that's not a great default, since guests will fail to
start if the hardware only supports GIC v3.

Change the behavior so that a sensible default is chosen instead.
That basically means using the same algorithm whether the user
didn't explicitly enable the GIC feature or they explicitly
enabled it but didn't specify any GIC version.
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

src/qemu/qemu_domain.c

@@ -2927,13 +2927,14 @@ static void
 qemuDomainDefEnableDefaultFeatures(virDomainDefPtr def,
                                    virQEMUCapsPtr qemuCaps)
 {
-    virGICVersion version;
-
-    /* The virt machine type always uses GIC: if the relevant element
+    /* The virt machine type always uses GIC: if the relevant information
      * was not included in the domain XML, we need to choose a suitable
      * GIC version ourselves */
-    if (def->features[VIR_DOMAIN_FEATURE_GIC] == VIR_TRISTATE_SWITCH_ABSENT &&
-        qemuDomainIsVirt(def)) {
+    if ((def->features[VIR_DOMAIN_FEATURE_GIC] == VIR_TRISTATE_SWITCH_ABSENT &&
+         qemuDomainIsVirt(def)) ||
+        (def->features[VIR_DOMAIN_FEATURE_GIC] == VIR_TRISTATE_SWITCH_ON &&
+         def->gic_version == VIR_GIC_VERSION_NONE)) {
+        virGICVersion version;
 
         VIR_DEBUG("Looking for usable GIC version in domain capabilities");
         for (version = VIR_GIC_VERSION_LAST - 1;
@@ -2948,9 +2949,6 @@ qemuDomainDefEnableDefaultFeatures(virDomainDefPtr def,
              * and rely on the code below to pick the default version, GICv2,
              * which supports all the features we need.
              *
-             * We'll want to revisit this once MSI support for GICv3 has been
-             * implemented in QEMU.
-             *
              * See https://bugzilla.redhat.com/show_bug.cgi?id=1414081 */
             if (version == VIR_GIC_VERSION_3 &&
                 def->virtType == VIR_DOMAIN_VIRT_QEMU) {
@@ -2967,17 +2965,17 @@ qemuDomainDefEnableDefaultFeatures(virDomainDefPtr def,
             }
         }
 
+        /* Use the default GIC version (GICv2) as a last-ditch attempt
+         * if no match could be found above */
+        if (def->gic_version == VIR_GIC_VERSION_NONE) {
+            VIR_DEBUG("Using GIC version 2 (default)");
+            def->gic_version = VIR_GIC_VERSION_2;
+        }
+
         /* Even if we haven't found a usable GIC version in the domain
          * capabilities, we still want to enable this */
         def->features[VIR_DOMAIN_FEATURE_GIC] = VIR_TRISTATE_SWITCH_ON;
     }
-
-    /* Use the default GIC version (GICv2) if no version was specified */
-    if (def->features[VIR_DOMAIN_FEATURE_GIC] == VIR_TRISTATE_SWITCH_ON &&
-        def->gic_version == VIR_GIC_VERSION_NONE) {
-        VIR_DEBUG("Using GIC version 2 (default)");
-        def->gic_version = VIR_GIC_VERSION_2;
-    }
 }
 
 

tests/qemuxml2argvdata/aarch64-gic-default-both.args

-aarch64-gic-v2.args
\ No newline at end of file
+aarch64-gic-v3.args
\ No newline at end of file

tests/qemuxml2argvdata/aarch64-gic-default-v3.args

-aarch64-gic-v2.args
\ No newline at end of file
+aarch64-gic-v3.args
\ No newline at end of file

tests/qemuxml2xmloutdata/aarch64-gic-default-both.xml

-../qemuxml2argvdata/aarch64-gic-v2.xml
\ No newline at end of file
+../qemuxml2argvdata/aarch64-gic-v3.xml
\ No newline at end of file

tests/qemuxml2xmloutdata/aarch64-gic-default-v3.xml

-../qemuxml2argvdata/aarch64-gic-v2.xml
\ No newline at end of file
+../qemuxml2argvdata/aarch64-gic-v3.xml
\ No newline at end of file