target/arm/cpu: Add the kvm-no-adjvtime CPU property

kvm-no-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>
Message-id: 20200120101023.16030-7-drjones@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

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 +173,39 @@ 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-no-adjvtime          By default kvm-no-adjvtime is disabled.  This
+                           means that by default the virtual time
+                           adjustment is enabled (vtime is *not not*
+                           adjusted).
+
+                           When virtual time adjustment is enabled each
+                           time the VM transitions back to running state
+                           the VCPU's virtual 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.  However it 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.
+
+                           Enable kvm-no-adjvtime to disable virtual time
+                           adjustment, also restoring the legacy (pre-5.0)
+                           behavior.
+
 SVE CPU Properties
 ==================
 

hw/arm/virt.c

@@ -1663,6 +1663,11 @@ static void machvirt_init(MachineState *machine)
             }
         }
 
+        if (vmc->kvm_no_adjvtime &&
+            object_property_find(cpuobj, "kvm-no-adjvtime", NULL)) {
+            object_property_set_bool(cpuobj, true, "kvm-no-adjvtime", NULL);
+        }
+
         if (vmc->no_pmu && object_property_find(cpuobj, "pmu", NULL)) {
             object_property_set_bool(cpuobj, false, "pmu", NULL);
         }
@@ -2153,8 +2158,11 @@ DEFINE_VIRT_MACHINE_AS_LATEST(5, 0)
 
 static void virt_machine_4_2_options(MachineClass *mc)
 {
+    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
+
     virt_machine_5_0_options(mc);
     compat_props_add(mc->compat_props, hw_compat_4_2, hw_compat_4_2_len);
+    vmc->kvm_no_adjvtime = true;
 }
 DEFINE_VIRT_MACHINE(4, 2)
 

include/hw/arm/virt.h

@@ -109,6 +109,7 @@ typedef struct {
     bool smbios_old_sys_ver;
     bool no_highmem_ecam;
     bool no_ged;   /* Machines < 4.2 has no support for ACPI GED device */
+    bool kvm_no_adjvtime;
 } VirtMachineClass;
 
 typedef struct {

target/arm/cpu.c

@@ -2551,6 +2551,7 @@ 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);
 
@@ -2743,6 +2744,7 @@ 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);
 }
 

target/arm/cpu64.c

@@ -605,6 +605,7 @@ 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;

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 +181,32 @@ void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
     env->features = arm_host_cpu_features.features;
 }
 
+static bool kvm_no_adjvtime_get(Object *obj, Error **errp)
+{
+    return !ARM_CPU(obj)->kvm_adjvtime;
+}
+
+static void kvm_no_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;
+    }
+
+    ARM_CPU(obj)->kvm_adjvtime = true;
+    object_property_add_bool(obj, "kvm-no-adjvtime", kvm_no_adjvtime_get,
+                             kvm_no_adjvtime_set, &error_abort);
+    object_property_set_description(obj, "kvm-no-adjvtime",
+                                    "Set on to disable the adjustment of "
+                                    "the virtual counter. VM stopped time "
+                                    "will be counted.", &error_abort);
+}
+
 bool kvm_arm_pmu_supported(CPUState *cpu)
 {
     return kvm_check_extension(cpu->kvm_state, KVM_CAP_ARM_PMU_V3);

target/arm/kvm_arm.h

@@ -255,6 +255,15 @@ void kvm_arm_sve_get_vls(CPUState *cs, unsigned long *map);
  */
 void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu);
 
+/**
+ * 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);
+
 /**
  * kvm_arm_aarch32_supported:
  * @cs: CPUState
@@ -345,6 +354,8 @@ 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;

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-no-adjvtime",
     NULL
 };
 

tests/qtest/arm-cpu-features.c

@@ -428,6 +428,8 @@ 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-no-adjvtime");
+
     if (g_str_equal(qtest_get_arch(), "aarch64")) {
         assert_has_feature_enabled(qts, "max", "aarch64");
         assert_has_feature_enabled(qts, "max", "sve");
@@ -462,6 +464,8 @@ static void test_query_cpu_model_expansion_kvm(const void *data)
         return;
     }
 
+    assert_has_feature_disabled(qts, "host", "kvm-no-adjvtime");
+
     if (g_str_equal(qtest_get_arch(), "aarch64")) {
         bool kvm_supports_sve;
         char max_name[8], name[8];