[Qemu-devel] [PULL 52/60] i386/cpu: make -cpu host support monitor/mwait

[Paolo Bonzini <pbonzini@redhat.com>]

From: "Michael S. Tsirkin" <mst@redhat.com>

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>
---
 accel/tcg/user-exec-stub.c |  3 +++
 target/i386/cpu.c          | 32 ++++++++++++++++++++++----------
 target/i386/cpu.h          |  9 +++++++++
 target/i386/kvm.c          |  9 +++++++++
 4 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/accel/tcg/user-exec-stub.c b/accel/tcg/user-exec-stub.c
index dbcf1ad..a32b449 100644
--- a/accel/tcg/user-exec-stub.c
+++ b/accel/tcg/user-exec-stub.c
@@ -2,6 +2,9 @@
 #include "qemu-common.h"
 #include "qom/cpu.h"
 #include "sysemu/replay.h"
+#include "sysemu/sysemu.h"
+
+bool enable_cpu_pm = false;
 
 void cpu_resume(CPUState *cpu)
 {
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index e6c2f8a..1e6a7d0 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;
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 16c59b7..8eaefee 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1382,6 +1382,15 @@ struct X86CPU {
     /* if true the CPUID code directly forward host cache leaves to the guest */
     bool cache_info_passthrough;
 
+    /* if true the CPUID code directly forwards
+     * host monitor/mwait leaves to the guest */
+    struct {
+        uint32_t eax;
+        uint32_t ebx;
+        uint32_t ecx;
+        uint32_t edx;
+    } mwait;
+
     /* Features that were filtered out because of missing host capabilities */
     uint32_t filtered_features[FEATURE_WORDS];
 
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index dc991f6..c5f72d6 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -366,6 +366,15 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
         if (!kvm_irqchip_in_kernel()) {
             ret &= ~CPUID_EXT_X2APIC;
         }
+
+        if (enable_cpu_pm) {
+            int disable_exits = kvm_check_extension(s,
+                                                    KVM_CAP_X86_DISABLE_EXITS);
+
+            if (disable_exits & KVM_X86_DISABLE_EXITS_MWAIT) {
+                ret |= CPUID_EXT_MONITOR;
+            }
+        }
     } else if (function == 6 && reg == R_EAX) {
         ret |= CPUID_6_EAX_ARAT; /* safe to allow because of emulated APIC */
     } else if (function == 7 && index == 0 && reg == R_EBX) {
-- 
1.8.3.1