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[libvirt] PATCH: recent qemu-kvm requires -enable-kvm flag to activate VT optimization



Hello,

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 slow as molasses ;)

I added a check in qemu_conf.c to see if `qemu -help` emits the -enable-kvm
flag, and if so, use the flag accordingly.

There exists a check in src/qemu/qemu_conf.c to check for the -no-kvm flag.
This check works the same way.
Adding the included code will not break systems where qemu does not
have the option.

See 'qemu -help':
...
-enable-kvm enable KVM full virtualization support ...

included patch against src/qemu/qemu_conf.{c,h}
-Steve


diff -ur libvirt/src/qemu/qemu_conf.c libvirt-qemu-enable-kvm/src/qemu/qemu_conf.c
--- libvirt/src/qemu/qemu_conf.c	2009-11-08 20:57:08.438908134 -0800
+++ libvirt-qemu-enable-kvm/src/qemu/qemu_conf.c	2009-11-08 22:36:04.299921427 -0800
@@ -1602,6 +1602,7 @@
     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;
@@ -1660,6 +1661,15 @@
         def->virtType == VIR_DOMAIN_VIRT_QEMU)
         disableKVM = 1;
 
+    /* Should explicitly enable KVM if
+     * 1. Guest domain is 'qemu'
+     * 2. The qemu binary has the -enable-kvm flag
+     * NOTE: user must be responsible to load the kvm modules
+     */
+    if ((qemuCmdFlags & QEMUD_CMD_FLAG_ENABLE_KVM) &&
+        def->virtType == VIR_DOMAIN_VIRT_QEMU)
+        enableKVM = 1;
+
     /*
      * Need to force a 32-bit guest CPU type if
      *
@@ -1787,6 +1797,8 @@
         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) {
diff -ur libvirt/src/qemu/qemu_conf.h libvirt-qemu-enable-kvm/src/qemu/qemu_conf.h
--- libvirt/src/qemu/qemu_conf.h	2009-11-08 20:57:08.438908134 -0800
+++ libvirt-qemu-enable-kvm/src/qemu/qemu_conf.h	2009-11-08 14:57:39.000000000 -0800
@@ -73,6 +73,7 @@
     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 */

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