[libvirt] [PATCH v2] Add invariant TSC cpu flag

[Ján Tomko]

Add suport for invariant TSC flag (CPUID 0x80000007, bit 8 of EDX).
If this flag is enabled, the TSC ticks at a constant rate across
all ACPI P-, C- and T-states.

This can be enabled by adding:
<feature name='invtsc'/>
to the <cpu> element.

Migration and saving the domain does not work with this flag.

QEMU support for this is not merged yet:
https://lists.gnu.org/archive/html/qemu-devel/2014-04/msg05024.html

The feature name "invtsc" differs from the name "" used by the linux kernel:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/cpu/powerflags.c?id=30321c7b#n18
---
v1: https://www.redhat.com/archives/libvir-list/2014-May/msg00183.html

 src/cpu/cpu_map.xml       |  5 +++++
 src/qemu/qemu_migration.c | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/src/cpu/cpu_map.xml b/src/cpu/cpu_map.xml
index 7d34d40..ffaeb92 100644
--- a/src/cpu/cpu_map.xml
+++ b/src/cpu/cpu_map.xml
@@ -327,6 +327,11 @@
       <cpuid function='0x00000007' ebx='0x00100000'/>
     </feature>
 
+    <!-- Advanced Power Management edx features -->
+    <feature name='invtsc'>
+      <cpuid function='0x80000007' edx='0x00000100'/>
+    </feature>
+
     <!-- models -->
     <model name='486'>
       <feature name='fpu'/>
diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
index a9f7fea..9ae3047 100644
--- a/src/qemu/qemu_migration.c
+++ b/src/qemu/qemu_migration.c
@@ -1513,6 +1513,20 @@ qemuMigrationIsAllowed(virQEMUDriverPtr driver, virDomainObjPtr vm,
         return false;
     }
 
+    for (i = 0; i < def->cpu->nfeatures; i++) {
+        virCPUFeatureDefPtr feature = &def->cpu->features[i];
+
+        if (feature->policy != VIR_CPU_FEATURE_REQUIRE)
+            continue;
+
+        if (STREQ(feature->name, "invtsc")) {
+            virReportError(VIR_ERR_OPERATION_INVALID,
+                           _("domain has CPU feature: %s"),
+                           feature->name);
+            return false;
+        }
+    }
+
     return true;
 }
 
-- 
1.8.3.2