Re: [PATCH] target/loongarch: Add paravirt preempt feature

[lixianglai]

Hi Bibo Mao:

Paravirt preempt feature is OnOffAuto type, it is disabled by default,
also the feature detection is added to check whether it is supported
on KVM host.

Signed-off-by: Bibo Mao <maob...@loongson.cn>
---
  target/loongarch/cpu.h     |  2 ++
  target/loongarch/kvm/kvm.c | 39 ++++++++++++++++++++++++++++++++++++++
  2 files changed, 41 insertions(+)

diff --git a/target/loongarch/cpu.h b/target/loongarch/cpu.h
index c592f69885..c6dad2417c 100644
--- a/target/loongarch/cpu.h
+++ b/target/loongarch/cpu.h
@@ -302,6 +302,7 @@ enum loongarch_features {
      LOONGARCH_FEATURE_STEALTIME,
      LOONGARCH_FEATURE_PTW,
      LOONGARCH_FEATURE_MSGINT,
+    LOONGARCH_FEATURE_PV_PREEMPT,
  };

typedef struct LoongArchBT {

@@ -464,6 +465,7 @@ struct ArchCPU {
      OnOffAuto msgint;
      OnOffAuto kvm_pv_ipi;
      OnOffAuto kvm_steal_time;
+    OnOffAuto kvm_pv_preempt;
      int32_t socket_id;  /* socket-id of this CPU */
      int32_t core_id;    /* core-id of this CPU */
      int32_t thread_id;  /* thread-id of this CPU */
diff --git a/target/loongarch/kvm/kvm.c b/target/loongarch/kvm/kvm.c
index 941142305e..7ca95181a1 100644
--- a/target/loongarch/kvm/kvm.c
+++ b/target/loongarch/kvm/kvm.c
@@ -1039,6 +1039,12 @@ static bool kvm_feature_supported(CPUState *cs, enum 
loongarch_features feature)
          ret = kvm_vm_ioctl(kvm_state, KVM_HAS_DEVICE_ATTR, &attr);
          return (ret == 0);

+ case LOONGARCH_FEATURE_PV_PREEMPT:

+        attr.group = KVM_LOONGARCH_VM_FEAT_CTRL;
+        attr.attr = KVM_LOONGARCH_VM_FEAT_PV_PREEMPT,
+        ret = kvm_vm_ioctl(kvm_state, KVM_HAS_DEVICE_ATTR, &attr);
+        return (ret == 0);
+
      default:
          return false;
      }
@@ -1203,6 +1209,21 @@ static int kvm_cpu_check_pv_features(CPUState *cs, Error 
**errp)
          env->pv_features |= BIT(KVM_FEATURE_STEAL_TIME);
      }

+ kvm_supported = kvm_feature_supported(cs, LOONGARCH_FEATURE_PV_PREEMPT);

+    if (cpu->kvm_pv_preempt == ON_OFF_AUTO_ON) {
+        if (!kvm_supported) {
+            error_setg(errp, "'pv preempt' feature not supported by KVM host");
+            return -ENOTSUP;
+        }
+    } else if (cpu->kvm_pv_preempt != ON_OFF_AUTO_AUTO) {
+        kvm_supported = false;
+    }
+
+    /* Feature preempt_hint depends on steal_time */
+    if (kvm_supported && (cpu->kvm_pv_preempt == ON_OFF_AUTO_ON)) {
+        env->pv_features |= BIT(KVM_FEATURE_PREEMPT);
+     }
+
      if (object_dynamic_cast(OBJECT(ms), TYPE_LOONGARCH_VIRT_MACHINE)) {
          LoongArchVirtMachineState *lvms = LOONGARCH_VIRT_MACHINE(ms);

@@ -1412,6 +1433,18 @@ static void kvm_steal_time_set(Object *obj, bool value, Error **errp)

      cpu->kvm_steal_time = value ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
  }

+static bool kvm_pv_preempt_get(Object *obj, Error **errp)

+{
+    return LOONGARCH_CPU(obj)->kvm_pv_preempt != ON_OFF_AUTO_OFF;
+}
+
+static void kvm_pv_preempt_set(Object *obj, bool value, Error **errp)
+{
+    LoongArchCPU *cpu = LOONGARCH_CPU(obj);
+
+    cpu->kvm_pv_preempt = value ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
+}
+
  void kvm_loongarch_cpu_post_init(LoongArchCPU *cpu)
  {
      cpu->lbt = ON_OFF_AUTO_AUTO;
@@ -1437,6 +1470,12 @@ void kvm_loongarch_cpu_post_init(LoongArchCPU *cpu)
                               kvm_steal_time_set);
      object_property_set_description(OBJECT(cpu), "kvm-steal-time",
                                      "Set off to disable KVM steal time.");
+
+    cpu->kvm_pv_preempt = ON_OFF_AUTO_OFF;
+    object_property_add_bool(OBJECT(cpu), "kvm-pv-preempt", kvm_pv_preempt_get,
+                             kvm_pv_preempt_set);
+    object_property_set_description(OBJECT(cpu), "kvm-pv-preempt",
+                                    "Set off to disable KVM paravirt 
preempt.");
  }

int kvm_arch_destroy_vcpu(CPUState *cs)

base-commit: c1c18d1e640b64292859ce9f30f3c344edfb0294

Reviewed-by:  Xianglai Li <lixiang...@loongson.cn>