i386/cpu: make -cpu host support monitor/mwait

When guest CPU PM is enabled, and with -cpu host, expose the host CPU
MWAIT leaf in the CPUID so guest can make good PM decisions.

Note: the result is 100% CPU utilization reported by host as host
no longer knows that the CPU is halted.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20180622192148.178309-3-mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 22 insertions, 10 deletions

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index e6c2f8a22a..1e6a7d0a75 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -3959,11 +3959,11 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         }
         break;
     case 5:
-        /* mwait info: needed for Core compatibility */
-        *eax = 0; /* Smallest monitor-line size in bytes */
-        *ebx = 0; /* Largest monitor-line size in bytes */
-        *ecx = CPUID_MWAIT_EMX | CPUID_MWAIT_IBE;
-        *edx = 0;
+        /* MONITOR/MWAIT Leaf */
+        *eax = cpu->mwait.eax; /* Smallest monitor-line size in bytes */
+        *ebx = cpu->mwait.ebx; /* Largest monitor-line size in bytes */
+        *ecx = cpu->mwait.ecx; /* flags */
+        *edx = cpu->mwait.edx; /* mwait substates */
         break;
     case 6:
         /* Thermal and Power Leaf */
@@ -4804,13 +4804,25 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
     Error *local_err = NULL;
     static bool ht_warned;
 
-    if (xcc->host_cpuid_required && !accel_uses_host_cpuid()) {
-        char *name = x86_cpu_class_get_model_name(xcc);
-        error_setg(&local_err, "CPU model '%s' requires KVM", name);
-        g_free(name);
-        goto out;
+    if (xcc->host_cpuid_required) {
+        if (!accel_uses_host_cpuid()) {
+            char *name = x86_cpu_class_get_model_name(xcc);
+            error_setg(&local_err, "CPU model '%s' requires KVM", name);
+            g_free(name);
+            goto out;
+        }
+
+        if (enable_cpu_pm) {
+            host_cpuid(5, 0, &cpu->mwait.eax, &cpu->mwait.ebx,
+                       &cpu->mwait.ecx, &cpu->mwait.edx);
+            env->features[FEAT_1_ECX] |= CPUID_EXT_MONITOR;
+        }
     }
 
+    /* mwait extended info: needed for Core compatibility */
+    /* We always wake on interrupt even if host does not have the capability */
+    cpu->mwait.ecx |= CPUID_MWAIT_EMX | CPUID_MWAIT_IBE;
+
     if (cpu->apic_id == UNASSIGNED_APIC_ID) {
         error_setg(errp, "apic-id property was not initialized properly");
         return;