qemu-kvm needs -enable-kvm flag for VT optimization

Recent qemu releases require command option '-enable-qemu' in order
for the kvm functionality be activated. Libvirt needs to pass this flag
to qemu when starting a domain. Note that without the option,
even if both the kernel and qemu support KVM, KVM will not be activated
and VMs will be very slow.

* src/qemu/qemu_conf.h src/qemu/qemu_conf.c: parse the extra command
  line option from help and add it when running kvm
* tests/qemuhelptest.c: this modified the flags output for qemu-0.10.5
  and qemu-kvm-0.11.0-rc2 regression tests

src/qemu/qemu_conf.c

@@ -878,6 +878,8 @@ static unsigned int qemudComputeCmdFlags(const char *help,
         flags |= QEMUD_CMD_FLAG_KQEMU;
     if (strstr(help, "-no-kvm"))
         flags |= QEMUD_CMD_FLAG_KVM;
+    if (strstr(help, "-enable-kvm"))
+        flags |= QEMUD_CMD_FLAG_ENABLE_KVM;
     if (strstr(help, "-no-reboot"))
         flags |= QEMUD_CMD_FLAG_NO_REBOOT;
     if (strstr(help, "-name"))
@@ -1595,6 +1597,7 @@ int qemudBuildCommandLine(virConnectPtr conn,
     struct utsname ut;
     int disableKQEMU = 0;
     int disableKVM = 0;
+    int enableKVM = 0;
     int qargc = 0, qarga = 0;
     const char **qargv = NULL;
     int qenvc = 0, qenva = 0;
@@ -1653,6 +1656,15 @@ int qemudBuildCommandLine(virConnectPtr conn,
         def->virtType == VIR_DOMAIN_VIRT_QEMU)
         disableKVM = 1;
 
+    /* Should explicitly enable KVM if
+     * 1. Guest domain is 'kvm'
+     * 2. The qemu binary has the -enable-kvm flag
+     * NOTE: user must be responsible for loading the kvm modules
+     */
+    if ((qemuCmdFlags & QEMUD_CMD_FLAG_ENABLE_KVM) &&
+        def->virtType == VIR_DOMAIN_VIRT_KVM)
+        enableKVM = 1;
+
     /*
      * Need to force a 32-bit guest CPU type if
      *
@@ -1780,6 +1792,8 @@ int qemudBuildCommandLine(virConnectPtr conn,
         ADD_ARG_LIT("-no-kqemu");
     if (disableKVM)
         ADD_ARG_LIT("-no-kvm");
+    if (enableKVM)
+        ADD_ARG_LIT("-enable-kvm");
     ADD_ARG_LIT("-m");
     ADD_ARG_LIT(memory);
     if (def->hugepage_backed) {

src/qemu/qemu_conf.h

@@ -73,6 +73,7 @@ enum qemud_cmd_flags {
     QEMUD_CMD_FLAG_XEN_DOMID     = (1 << 20), /* -xen-domid (new style xen integration) */
     QEMUD_CMD_FLAG_MIGRATE_QEMU_UNIX = (1 << 21), /* Does qemu support unix domain sockets for migration? */
     QEMUD_CMD_FLAG_CHARDEV       = (1 << 22), /* Is the new -chardev arg available */
+    QEMUD_CMD_FLAG_ENABLE_KVM    = (1 << 23), /* Is the -enable-kvm flag available to "enable KVM full virtualization support" */
 };
 
 /* Main driver state */

tests/qemuhelptest.c

@@ -121,7 +121,8 @@ mymain(int argc, char **argv)
             QEMUD_CMD_FLAG_DRIVE_FORMAT |
             QEMUD_CMD_FLAG_DRIVE_SERIAL |
             QEMUD_CMD_FLAG_VGA |
-            QEMUD_CMD_FLAG_0_10,
+            QEMUD_CMD_FLAG_0_10 |
+            QEMUD_CMD_FLAG_ENABLE_KVM,
             10005, 0,  0);
     DO_TEST("qemu-kvm-0.10.5",
             QEMUD_CMD_FLAG_VNC_COLON |
@@ -177,7 +178,8 @@ mymain(int argc, char **argv)
             QEMUD_CMD_FLAG_VGA |
             QEMUD_CMD_FLAG_0_10 |
             QEMUD_CMD_FLAG_PCIDEVICE |
-            QEMUD_CMD_FLAG_MEM_PATH,
+            QEMUD_CMD_FLAG_MEM_PATH |
+            QEMUD_CMD_FLAG_ENABLE_KVM,
             10092, 1,  0);
 
     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;