qemu: Drop disabled CPU features unknown to QEMU

When a CPU definition wants to explicitly disable some features that are
unknown to QEMU, we can safely drop them from the definition before
starting QEMU. Naturally QEMU won't enable such features implicitly.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

src/qemu/qemu_process.c

@@ -6047,6 +6047,26 @@ qemuProcessSetupHotpluggableVcpus(virQEMUDriverPtr driver,
 }
 
 
+static bool
+qemuProcessDropUnknownCPUFeatures(const char *name,
+                                  virCPUFeaturePolicy policy,
+                                  void *opaque)
+{
+    const char **features = opaque;
+
+    if (policy != VIR_CPU_FEATURE_DISABLE &&
+        policy != VIR_CPU_FEATURE_FORBID)
+        return true;
+
+    if (virStringListHasString(features, name))
+        return true;
+
+    /* Features unknown to QEMU are implicitly disabled, we can just drop them
+     * from the definition. */
+    return false;
+}
+
+
 static int
 qemuProcessUpdateGuestCPU(virDomainDefPtr def,
                           virQEMUCapsPtr qemuCaps,
@@ -6112,6 +6132,18 @@ qemuProcessUpdateGuestCPU(virDomainDefPtr def,
                                 &def->os.arch) < 0)
         return -1;
 
+    if (ARCH_IS_X86(def->os.arch)) {
+        VIR_AUTOSTRINGLIST features = NULL;
+
+        if (virQEMUCapsGetCPUFeatures(qemuCaps, def->virtType, false, &features) < 0)
+            return -1;
+
+        if (features &&
+            virCPUDefFilterFeatures(def->cpu, qemuProcessDropUnknownCPUFeatures,
+                                    features) < 0)
+            return -1;
+    }
+
     return 0;
 }
 

tests/qemuxml2argvdata/cpu-Icelake-Server-pconfig.x86_64-latest.args

@@ -13,7 +13,7 @@ QEMU_AUDIO_DRV=none \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-test/master-key.aes \
 -machine pc,accel=kvm,usb=off,dump-guest-core=off \
--cpu Icelake-Server,pconfig=off \
+-cpu Icelake-Server \
 -m 214 \
 -overcommit mem-lock=off \
 -smp 1,sockets=1,cores=1,threads=1 \