[Qemu-devel] [PATCH v2 9/9] i386/kvm: add support for Direct Mode for Hyper-V synthetic timers

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Hyper-V on KVM can only use Synthetic timers with Direct Mode (opting for
an interrupt instead of VMBus message). This new capability is only
announced in KVM_GET_SUPPORTED_HV_CPUID.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 docs/hyperv.txt            | 10 ++++++++++
 target/i386/cpu.c          |  2 ++
 target/i386/cpu.h          |  1 +
 target/i386/hyperv-proto.h |  1 +
 target/i386/kvm.c          |  9 +++++++++
 5 files changed, 23 insertions(+)

diff --git a/docs/hyperv.txt b/docs/hyperv.txt
index beadb2d0d4..8fdf25c829 100644
--- a/docs/hyperv.txt
+++ b/docs/hyperv.txt
@@ -174,6 +174,16 @@ without the feature to find out if enabling it is beneficial.
 
 Requires: hv-vapic
 
+3.17. hv-stimer-direct
+=======================
+Hyper-V specification allows synthetic timer operation in two modes: "classic",
+when expiration event is delivered as SynIC message and "direct", when the event
+is delivered via normal interrupt. It is known that nested Hyper-V can only
+use synthetic timers in direct mode and thus 'hv-stimer-direct' needs to be
+enabled.
+
+Requires: hv-vpindex, hv-synic, hv-time, hv-stimer
+
 
 4. Development features
 ========================
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 063551ef55..3cfd85758c 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5849,6 +5849,8 @@ static Property x86_cpu_properties[] = {
                       HYPERV_FEAT_EVMCS, 0),
     DEFINE_PROP_BIT64("hv-ipi", X86CPU, hyperv_features,
                       HYPERV_FEAT_IPI, 0),
+    DEFINE_PROP_BIT64("hv-stimer-direct", X86CPU, hyperv_features,
+                      HYPERV_FEAT_STIMER_DIRECT, 0),
     DEFINE_PROP_BOOL("hv-passthrough", X86CPU, hyperv_passthrough, false),
 
     DEFINE_PROP_BOOL("check", X86CPU, check_cpuid, true),
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 1f1f8969b4..0b6b781ecb 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -758,6 +758,7 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS];
 #define HYPERV_FEAT_TLBFLUSH            11
 #define HYPERV_FEAT_EVMCS               12
 #define HYPERV_FEAT_IPI                 13
+#define HYPERV_FEAT_STIMER_DIRECT       14
 
 #ifndef HYPERV_SPINLOCK_NEVER_RETRY
 #define HYPERV_SPINLOCK_NEVER_RETRY             0xFFFFFFFF
diff --git a/target/i386/hyperv-proto.h b/target/i386/hyperv-proto.h
index c0272b3a01..cffac10b45 100644
--- a/target/i386/hyperv-proto.h
+++ b/target/i386/hyperv-proto.h
@@ -49,6 +49,7 @@
 #define HV_GUEST_IDLE_STATE_AVAILABLE           (1u << 5)
 #define HV_FREQUENCY_MSRS_AVAILABLE             (1u << 8)
 #define HV_GUEST_CRASH_MSR_AVAILABLE            (1u << 10)
+#define HV_STIMER_DIRECT_MODE_AVAILABLE         (1u << 19)
 
 /*
  * HV_CPUID_ENLIGHTMENT_INFO.EAX bits
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 7ae2f63f72..fb29a3057b 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -803,6 +803,14 @@ static struct {
         },
         .dependencies = BIT(HYPERV_FEAT_VPINDEX)
     },
+    [HYPERV_FEAT_STIMER_DIRECT] = {
+        .desc = "direct mode synthetic timers (hv-stimer-direct)",
+        .flags = {
+            {.fw = FEAT_HYPERV_EDX,
+             .bits = HV_STIMER_DIRECT_MODE_AVAILABLE}
+        },
+        .dependencies = BIT(HYPERV_FEAT_STIMER)
+    },
 };
 
 static struct kvm_cpuid2 *try_get_hv_cpuid(CPUState *cs, int max)
@@ -1125,6 +1133,7 @@ static int hyperv_handle_properties(CPUState *cs,
     r |= hv_cpuid_check_and_set(cs, cpuid, HYPERV_FEAT_TLBFLUSH);
     r |= hv_cpuid_check_and_set(cs, cpuid, HYPERV_FEAT_EVMCS);
     r |= hv_cpuid_check_and_set(cs, cpuid, HYPERV_FEAT_IPI);
+    r |= hv_cpuid_check_and_set(cs, cpuid, HYPERV_FEAT_STIMER_DIRECT);
 
     /* Additional dependencies not covered by kvm_hyperv_properties[] */
     if (hyperv_feat_enabled(cpu, HYPERV_FEAT_SYNIC) &&
-- 
2.20.1