i386: Implement pseudo 'hv-avic' ('hv-apicv') enlightenment

The enlightenment allows to use Hyper-V SynIC with hardware APICv/AVIC
enabled. Normally, Hyper-V SynIC disables these hardware features and
suggests the guest to use paravirtualized AutoEOI feature. Linux-4.15
gains support for conditional APICv/AVIC disablement, the feature
stays on until the guest tries to use AutoEOI feature with SynIC. With
'HV_DEPRECATING_AEOI_RECOMMENDED' bit exposed, modern enough Windows/
Hyper-V versions should follow the recommendation and not use the
(unwanted) feature.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210902093530.345756-7-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

5 files changed, 24 insertions, 2 deletions

diff --git a/docs/hyperv.txt b/docs/hyperv.txt
index 072709a..cd1ea3b 100644
--- a/docs/hyperv.txt
+++ b/docs/hyperv.txt
@@ -189,7 +189,15 @@ enabled.
 
 Requires: hv-vpindex, hv-synic, hv-time, hv-stimer
 
-3.17. hv-no-nonarch-coresharing=on/off/auto
+3.18. hv-avic (hv-apicv)
+=======================
+The enlightenment allows to use Hyper-V SynIC with hardware APICv/AVIC enabled.
+Normally, Hyper-V SynIC disables these hardware feature and suggests the guest
+to use paravirtualized AutoEOI feature.
+Note: enabling this feature on old hardware (without APICv/AVIC support) may
+have negative effect on guest's performace.
+
+3.19. hv-no-nonarch-coresharing=on/off/auto
 ===========================================
 This enlightenment tells guest OS that virtual processors will never share a
 physical core unless they are reported as sibling SMT threads. This information
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 2a19eba..8154343 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6644,6 +6644,8 @@ static void x86_cpu_initfn(Object *obj)
     object_property_add_alias(obj, "sse4_1", obj, "sse4.1");
     object_property_add_alias(obj, "sse4_2", obj, "sse4.2");
 
+    object_property_add_alias(obj, "hv-apicv", obj, "hv-avic");
+
     if (xcc->model) {
         x86_cpu_load_model(cpu, xcc->model);
     }
@@ -6831,6 +6833,8 @@ static Property x86_cpu_properties[] = {
                       HYPERV_FEAT_IPI, 0),
     DEFINE_PROP_BIT64("hv-stimer-direct", X86CPU, hyperv_features,
                       HYPERV_FEAT_STIMER_DIRECT, 0),
+    DEFINE_PROP_BIT64("hv-avic", X86CPU, hyperv_features,
+                      HYPERV_FEAT_AVIC, 0),
     DEFINE_PROP_ON_OFF_AUTO("hv-no-nonarch-coresharing", X86CPU,
                             hyperv_no_nonarch_cs, ON_OFF_AUTO_OFF),
     DEFINE_PROP_BOOL("hv-passthrough", X86CPU, hyperv_passthrough, false),
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 8a7209b..65f0ee2 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1056,6 +1056,7 @@ typedef uint64_t FeatureWordArray[FEATURE_WORDS];
 #define HYPERV_FEAT_EVMCS               12
 #define HYPERV_FEAT_IPI                 13
 #define HYPERV_FEAT_STIMER_DIRECT       14
+#define HYPERV_FEAT_AVIC                15
 
 #ifndef HYPERV_SPINLOCK_NEVER_NOTIFY
 #define HYPERV_SPINLOCK_NEVER_NOTIFY             0xFFFFFFFF
diff --git a/target/i386/kvm/hyperv-proto.h b/target/i386/kvm/hyperv-proto.h
index 5fbb385..89f81af 100644
--- a/target/i386/kvm/hyperv-proto.h
+++ b/target/i386/kvm/hyperv-proto.h
@@ -66,6 +66,7 @@
 #define HV_APIC_ACCESS_RECOMMENDED          (1u << 3)
 #define HV_SYSTEM_RESET_RECOMMENDED         (1u << 4)
 #define HV_RELAXED_TIMING_RECOMMENDED       (1u << 5)
+#define HV_DEPRECATING_AEOI_RECOMMENDED     (1u << 9)
 #define HV_CLUSTER_IPI_RECOMMENDED          (1u << 10)
 #define HV_EX_PROCESSOR_MASKS_RECOMMENDED   (1u << 11)
 #define HV_ENLIGHTENED_VMCS_RECOMMENDED     (1u << 14)
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index a9a8f77..68faf72 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -924,6 +924,13 @@ static struct {
         },
         .dependencies = BIT(HYPERV_FEAT_STIMER)
     },
+    [HYPERV_FEAT_AVIC] = {
+        .desc = "AVIC/APICv support (hv-avic/hv-apicv)",
+        .flags = {
+            {.func = HV_CPUID_ENLIGHTMENT_INFO, .reg = R_EAX,
+             .bits = HV_DEPRECATING_AEOI_RECOMMENDED}
+        }
+    },
 };
 
 static struct kvm_cpuid2 *try_get_hv_cpuid(CPUState *cs, int max,
@@ -1373,7 +1380,8 @@ static int hyperv_fill_cpuids(CPUState *cs,
     c->eax = hv_build_cpuid_leaf(cs, HV_CPUID_ENLIGHTMENT_INFO, R_EAX);
     c->ebx = cpu->hyperv_spinlock_attempts;
 
-    if (hyperv_feat_enabled(cpu, HYPERV_FEAT_VAPIC)) {
+    if (hyperv_feat_enabled(cpu, HYPERV_FEAT_VAPIC) &&
+        !hyperv_feat_enabled(cpu, HYPERV_FEAT_AVIC)) {
         c->eax |= HV_APIC_ACCESS_RECOMMENDED;
     }