Implement Hardware page table walker(PTW for short) feature in KVM mode.
Use OnOffAuto type variable ptw to check the PTW feature. If the PTW
feature is not supported on KVM host, there is error reported with ptw=on
option.

By default PTW feature is disabled on la464 CPU type, and auto detected
on max CPU type.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
---
 target/loongarch/cpu.c     |  6 +++---
 target/loongarch/cpu.h     |  1 +
 target/loongarch/kvm/kvm.c | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/target/loongarch/cpu.c b/target/loongarch/cpu.c
index e80a92fb2e..d74c3c3766 100644
--- a/target/loongarch/cpu.c
+++ b/target/loongarch/cpu.c
@@ -236,7 +236,7 @@ static void loongarch_set_ptw(Object *obj, bool value, Error **errp)
     cpu->ptw = value ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
 
     if (kvm_enabled()) {
-        /* PTW feature is only support in TCG mode now */
+        /* kvm feature detection in function kvm_arch_init_vcpu */
         return;
     }
 
@@ -406,14 +406,14 @@ static void loongarch_la132_initfn(Object *obj)
 static void loongarch_max_initfn(Object *obj)
 {
     LoongArchCPU *cpu = LOONGARCH_CPU(obj);
-    /* '-cpu max' for TCG: we use cpu la464. */
+    /* '-cpu max': use it for max supported CPU features */
     loongarch_la464_initfn(obj);
 
+    cpu->ptw = ON_OFF_AUTO_AUTO;
     if (tcg_enabled()) {
         cpu->env.cpucfg[1] = FIELD_DP32(cpu->env.cpucfg[1], CPUCFG1, MSG_INT, 1);
         cpu->msgint = ON_OFF_AUTO_AUTO;
         cpu->env.cpucfg[2] = FIELD_DP32(cpu->env.cpucfg[2], CPUCFG2, HPTW, 1);
-        cpu->ptw = ON_OFF_AUTO_AUTO;
     }
 }
 
diff --git a/target/loongarch/cpu.h b/target/loongarch/cpu.h
index b1d6799222..1a14469b3b 100644
--- a/target/loongarch/cpu.h
+++ b/target/loongarch/cpu.h
@@ -279,6 +279,7 @@ enum loongarch_features {
     LOONGARCH_FEATURE_PMU,
     LOONGARCH_FEATURE_PV_IPI,
     LOONGARCH_FEATURE_STEALTIME,
+    LOONGARCH_FEATURE_PTW,
 };
 
 typedef struct  LoongArchBT {
diff --git a/target/loongarch/kvm/kvm.c b/target/loongarch/kvm/kvm.c
index 4e4f4e79f6..26e40c9bdc 100644
--- a/target/loongarch/kvm/kvm.c
+++ b/target/loongarch/kvm/kvm.c
@@ -931,6 +931,12 @@ 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_PTW:
+        attr.group = KVM_LOONGARCH_VM_FEAT_CTRL;
+        attr.attr = KVM_LOONGARCH_VM_FEAT_PTW;
+        ret = kvm_vm_ioctl(kvm_state, KVM_HAS_DEVICE_ATTR, &attr);
+        return (ret == 0);
+
     default:
         return false;
     }
@@ -1029,6 +1035,29 @@ static int kvm_cpu_check_pmu(CPUState *cs, Error **errp)
     return 0;
 }
 
+static int kvm_cpu_check_ptw(CPUState *cs, Error **errp)
+{
+    LoongArchCPU *cpu = LOONGARCH_CPU(cs);
+    CPULoongArchState *env = cpu_env(cs);
+    bool kvm_supported;
+
+    kvm_supported = kvm_feature_supported(cs, LOONGARCH_FEATURE_PTW);
+    if (cpu->ptw == ON_OFF_AUTO_ON) {
+        if (!kvm_supported) {
+            error_setg(errp, "'ptw' feature not supported by KVM on the host");
+            return -ENOTSUP;
+        }
+    } else if (cpu->ptw != ON_OFF_AUTO_AUTO) {
+        /* disable pmu if ON_OFF_AUTO_OFF is set */
+        kvm_supported = false;
+    }
+
+    if (kvm_supported) {
+        env->cpucfg[2] = FIELD_DP32(env->cpucfg[2], CPUCFG2, HPTW, 1);
+    }
+    return 0;
+}
+
 static int kvm_cpu_check_pv_features(CPUState *cs, Error **errp)
 {
     MachineState *ms = MACHINE(qdev_get_machine());
@@ -1123,6 +1152,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
         return ret;
     }
 
+    ret = kvm_cpu_check_ptw(cs, &local_err);
+    if (ret < 0) {
+        error_report_err(local_err);
+        return ret;
+    }
+
     return 0;
 }
 
-- 
2.39.3