qemu: Ignore fallback CPU attribute on reconnect

When reconnecting to a running domain with host-model CPU started by old
libvirt which did not store the actual CPU in the status XML, we need to
ignore the fallback attribute to make sure we can translate the detected
host CPU model to a model which is supported by the running QEMU.

https://bugzilla.redhat.com/show_bug.cgi?id=1532980Signed-off-by: NJiri Denemark <jdenemar@redhat.com>
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>

src/qemu/qemu_process.c

@@ -3887,6 +3887,11 @@ qemuProcessUpdateCPU(virQEMUDriverPtr driver,
     virDomainCapsCPUModelsPtr models = NULL;
     int ret = -1;
 
+    /* The host CPU model comes from host caps rather than QEMU caps so
+     * fallback must be allowed no matter what the user specified in the XML.
+     */
+    vm->def->cpu->fallback = VIR_CPU_FALLBACK_ALLOW;
+
     if (qemuProcessFetchGuestCPU(driver, vm, asyncJob, &cpu, &disabled) < 0)
         goto cleanup;