[Qemu-devel] [QEMU 1.2 PATCH] i386: kvm: have a predefined set of default KVM feature bits

[Eduardo Habkost <ehabkost@redhat.com>]

We can't simply expose the GET_SUPPORTED_CPUID results directly to the
guest, or the resulting guest-visible CPUID bits may change under the
guest's feet when we live-migrate.

We still have to implement proper per-machine-type migration
compatibility bits, but this at least is a workaround for cases where PV
EOI would be silently enabled after a host kernel upgrade.

We also have to implement proper check/warnings about unsupported bits
when using "-cpu check" or "-cpu enforce", because the default bits may
be silently disabled if the host kernel doesn't support them.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 target-i386/cpu.c | 18 +++++++++++++++++-
 target-i386/cpu.h | 10 ++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 120a2e3..52042f0 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -283,6 +283,21 @@ typedef struct x86_def_t {
           CPUID_EXT3_CR8LEG | CPUID_EXT3_ABM | CPUID_EXT3_SSE4A)
 #define TCG_SVM_FEATURES 0
 
+
+/* List of KVM features we (try to) enable by default
+ * 
+ * CPUID_KVM_PV_EOI is not enabled until we have proper per-machine-type
+ * migration compatibility support
+ * 
+ * CPUID_KVM_MMU is not enabled because it is deprecated.
+ */
+#define DEFAULT_KVM_FEATURES (CPUID_KVM_CLOCKSOURCE | \
+                              CPUID_KVM_KVM_NOP_IO_DELAY | \
+                              CPUID_KVM_CLOCKSOURCE2 | \
+                              CPUID_KVM_KVM_ASYNC_PF | \
+                              CPUID_KVM_STEAL_TIME | \
+                              CPUID_KVM_CLOCKSOURCE_STABLE_BIT)
+
 /* maintains list of cpu model definitions
  */
 static x86_def_t *x86_defs = {NULL};
@@ -887,7 +902,8 @@ static int cpu_x86_find_by_name(x86_def_t *x86_cpu_def, const char *cpu_model)
         memcpy(x86_cpu_def, def, sizeof(*def));
     }
 
-    plus_kvm_features = ~0; /* not supported bits will be filtered out later */
+    /* not supported bits will be filtered out later */
+    plus_kvm_features = DEFAULT_KVM_FEATURES;
 
     add_flagname_to_bitmaps("hypervisor", &plus_features,
         &plus_ext_features, &plus_ext2_features, &plus_ext3_features,
diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index 60f9e97..5ce4baf 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -440,6 +440,16 @@
 #define CPUID_SVM_PAUSEFILTER  (1 << 10)
 #define CPUID_SVM_PFTHRESHOLD  (1 << 12)
 
+/* CPUID[4000_0001h].EAX bits: */
+#define CPUID_KVM_CLOCKSOURCE             (1 << 0)
+#define CPUID_KVM_KVM_NOP_IO_DELAY        (1 << 1)
+#define CPUID_KVM_MMU                     (1 << 2)
+#define CPUID_KVM_CLOCKSOURCE2            (1 << 3)
+#define CPUID_KVM_KVM_ASYNC_PF            (1 << 4)
+#define CPUID_KVM_STEAL_TIME              (1 << 5)
+#define CPUID_KVM_KVM_PV_EOI              (1 << 6)
+#define CPUID_KVM_CLOCKSOURCE_STABLE_BIT  (1 << 24)
+
 #define CPUID_VENDOR_INTEL_1 0x756e6547 /* "Genu" */
 #define CPUID_VENDOR_INTEL_2 0x49656e69 /* "ineI" */
 #define CPUID_VENDOR_INTEL_3 0x6c65746e /* "ntel" */
-- 
1.7.11.4