[RFC PATCH 5/5] target/arm/cpu: Add the kvm-adjvtime CPU property

[Andrew Jones <drjones@redhat.com>]

kvm-adjvtime is a KVM specific CPU property and a first of its kind.
To accommodate it we also add kvm_arm_add_vcpu_properties() and a
KVM specific CPU properties description to the CPU features document.

Signed-off-by: Andrew Jones <drjones@redhat.com>
---
 docs/arm-cpu-features.rst | 27 ++++++++++++++++++++++++++-
 target/arm/cpu.c          |  2 ++
 target/arm/cpu64.c        |  1 +
 target/arm/kvm.c          | 27 +++++++++++++++++++++++++++
 target/arm/kvm_arm.h      | 11 +++++++++++
 target/arm/monitor.c      |  1 +
 tests/arm-cpu-features.c  |  4 ++++
 7 files changed, 72 insertions(+), 1 deletion(-)

diff --git a/docs/arm-cpu-features.rst b/docs/arm-cpu-features.rst
index 1b367e22e16e..5c317296845f 100644
--- a/docs/arm-cpu-features.rst
+++ b/docs/arm-cpu-features.rst
@@ -31,7 +31,9 @@ supporting the feature or only supporting the feature under certain
 configurations.  For example, the `aarch64` CPU feature, which, when
 disabled, enables the optional AArch32 CPU feature, is only supported
 when using the KVM accelerator and when running on a host CPU type that
-supports the feature.
+supports the feature.  While `aarch64` currently only works with KVM,
+it could work with TCG.  CPU features that are specific to KVM are
+prefixed with "kvm-" and are described in "KVM VCPU Features".
 
 CPU Feature Probing
 ===================
@@ -171,6 +173,29 @@ disabling many SVE vector lengths would be quite verbose, the `sve<N>` CPU
 properties have special semantics (see "SVE CPU Property Parsing
 Semantics").
 
+KVM VCPU Features
+=================
+
+KVM VCPU features are CPU features that are specific to KVM, such as
+paravirt features or features that enable CPU virtualization extensions.
+The features' CPU properties are only available when KVM is enabled and are
+named with the prefix "kvm-".  KVM VCPU features may be probed, enabled, and
+disabled in the same way as other CPU features.  Below is the list of KVM
+VCPU features and their descriptions.
+
+  kvm-adjvtime             When enabled, each time the VM transitions back
+                           to running state the VCPU's vitual counter is
+                           updated to ensure stopped time is not counted.
+                           This avoids time jumps surprising guest OSes and
+                           applications, as long as they use the virtual
+                           counter for timekeeping, but has the side effect
+                           of the virtual and physical counters diverging.
+                           All timekeeping based on the virtual counter will
+                           appear to lag behind any timekeeping that does
+                           not subtract VM stopped time.  The guest may
+                           resynchronize its virtual counter with other time
+                           sources as needed.
+
 SVE CPU Properties
 ==================
 
diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 7695ae551218..d8ad26438f9f 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -2483,6 +2483,7 @@ static void arm_max_initfn(Object *obj)
 
     if (kvm_enabled()) {
         kvm_arm_set_cpu_features_from_host(cpu);
+        kvm_arm_add_vcpu_properties(obj);
     } else {
         cortex_a15_initfn(obj);
 
@@ -2674,6 +2675,7 @@ static void arm_host_initfn(Object *obj)
     if (arm_feature(&cpu->env, ARM_FEATURE_AARCH64)) {
         aarch64_add_sve_properties(obj);
     }
+    kvm_arm_add_vcpu_properties(obj);
     arm_cpu_post_init(obj);
 }
 
diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 68baf0482ffa..c9a657a178ce 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -620,6 +620,7 @@ static void aarch64_max_initfn(Object *obj)
 
     if (kvm_enabled()) {
         kvm_arm_set_cpu_features_from_host(cpu);
+        kvm_arm_add_vcpu_properties(obj);
     } else {
         uint64_t t;
         uint32_t u;
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index f79b9b8ef57a..1652e3febe51 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -17,6 +17,8 @@
 #include "qemu/timer.h"
 #include "qemu/error-report.h"
 #include "qemu/main-loop.h"
+#include "qom/object.h"
+#include "qapi/error.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/kvm.h"
 #include "sysemu/kvm_int.h"
@@ -179,6 +181,31 @@ void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
     env->features = arm_host_cpu_features.features;
 }
 
+static bool kvm_adjvtime_get(Object *obj, Error **errp)
+{
+    return ARM_CPU(obj)->kvm_adjvtime;
+}
+
+static void kvm_adjvtime_set(Object *obj, bool value, Error **errp)
+{
+    ARM_CPU(obj)->kvm_adjvtime = value;
+}
+
+/* KVM VCPU properties should be prefixed with "kvm-". */
+void kvm_arm_add_vcpu_properties(Object *obj)
+{
+    if (!kvm_enabled()) {
+        return;
+    }
+
+    object_property_add_bool(obj, "kvm-adjvtime", kvm_adjvtime_get,
+                             kvm_adjvtime_set, &error_abort);
+    object_property_set_description(obj, "kvm-adjvtime",
+                                    "Set on to enable the adjustment of "
+                                    "the virtual counter. VM stopped time "
+                                    "will not be counted.", &error_abort);
+}
+
 bool kvm_arm_pmu_supported(CPUState *cpu)
 {
     KVMState *s = KVM_STATE(current_machine->accelerator);
diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
index d506c4e84be6..5d8077df6a4a 100644
--- a/target/arm/kvm_arm.h
+++ b/target/arm/kvm_arm.h
@@ -232,6 +232,15 @@ void kvm_arm_sve_get_vls(CPUState *cs, unsigned long *map);
  */
 void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu);
 
+/**
+ * void kvm_arm_add_vcpu_properties:
+ * @obj: The CPU object to add the properties to
+ *
+ * Add all KVM specific CPU properties to the CPU object. These
+ * are the CPU properties with "kvm-" prefixed names.
+ */
+void kvm_arm_add_vcpu_properties(Object *obj);
+
 /**
  * void kvm_arm_set_virtual_time:
  * @cs: CPUState
@@ -308,6 +317,8 @@ static inline void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
     cpu->host_cpu_probe_failed = true;
 }
 
+static inline void kvm_arm_add_vcpu_properties(Object *obj) {}
+
 static inline bool kvm_arm_aarch32_supported(CPUState *cs)
 {
     return false;
diff --git a/target/arm/monitor.c b/target/arm/monitor.c
index e912ed2cefa0..a89976fe7e4b 100644
--- a/target/arm/monitor.c
+++ b/target/arm/monitor.c
@@ -103,6 +103,7 @@ static const char *cpu_model_advertised_features[] = {
     "sve128", "sve256", "sve384", "sve512",
     "sve640", "sve768", "sve896", "sve1024", "sve1152", "sve1280",
     "sve1408", "sve1536", "sve1664", "sve1792", "sve1920", "sve2048",
+    "kvm-adjvtime",
     NULL
 };
 
diff --git a/tests/arm-cpu-features.c b/tests/arm-cpu-features.c
index ee444b04010f..c207a2bec9e9 100644
--- a/tests/arm-cpu-features.c
+++ b/tests/arm-cpu-features.c
@@ -417,6 +417,8 @@ static void test_query_cpu_model_expansion(const void *data)
     assert_has_feature_enabled(qts, "cortex-a15", "pmu");
     assert_has_not_feature(qts, "cortex-a15", "aarch64");
 
+    assert_has_not_feature(qts, "max", "kvm-adjvtime");
+
     if (g_str_equal(qtest_get_arch(), "aarch64")) {
         assert_has_feature_enabled(qts, "max", "aarch64");
         assert_has_feature_enabled(qts, "max", "sve");
@@ -445,6 +447,8 @@ static void test_query_cpu_model_expansion_kvm(const void *data)
 
     assert_has_feature_enabled(qts, "host", "pmu");
 
+    assert_has_feature_disabled(qts, "host", "kvm-adjvtime");
+
     if (g_str_equal(qtest_get_arch(), "aarch64")) {
         bool kvm_supports_sve;
         char max_name[8], name[8];
-- 
2.20.1