[PULL 16/17] i386: Hyper-V Direct TLB flush hypercall

[Paolo Bonzini]

From: Vitaly Kuznetsov <vkuznets@redhat.com>

Hyper-V TLFS allows for L0 and L1 hypervisors to collaborate on L2's
TLB flush hypercalls handling. With the correct setup, L2's TLB flush
hypercalls can be handled by L0 directly, without the need to exit to
L1.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220525115949.1294004-6-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 docs/hyperv.txt                | 11 +++++++++++
 target/i386/cpu.h              |  1 +
 target/i386/kvm/hyperv-proto.h |  1 +
 target/i386/cpu.c              |  2 ++
 target/i386/kvm/kvm.c          |  8 ++++++++
 5 files changed, 23 insertions(+)

diff --git a/docs/hyperv.txt b/docs/hyperv.txt
index 4b132b1c94..14a7f449ea 100644
--- a/docs/hyperv.txt
+++ b/docs/hyperv.txt
@@ -262,6 +262,17 @@ Allow for extended GVA ranges to be passed to Hyper-V TLB 
flush hypercalls
 
 Requires: hv-tlbflush
 
+3.25. hv-tlbflush-direct
+=========================
+The enlightenment is nested specific, it targets Hyper-V on KVM guests. When
+enabled, it allows L0 (KVM) to directly handle TLB flush hypercalls from L2
+guest without the need to exit to L1 (Hyper-V) hypervisor. While the feature is
+supported for both VMX (Intel) and SVM (AMD), the VMX implementation requires
+Enlightened VMCS ('hv-evmcs') feature to also be enabled.
+
+Requires: hv-vapic
+Recommended: hv-evmcs (Intel)
+
 4. Supplementary features
 =========================
 
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 5ff48257e5..82004b65b9 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1109,6 +1109,7 @@ uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
 #define HYPERV_FEAT_MSR_BITMAP          17
 #define HYPERV_FEAT_XMM_INPUT           18
 #define HYPERV_FEAT_TLBFLUSH_EXT        19
+#define HYPERV_FEAT_TLBFLUSH_DIRECT     20
 
 #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 c7854ed6d3..464fbf09e3 100644
--- a/target/i386/kvm/hyperv-proto.h
+++ b/target/i386/kvm/hyperv-proto.h
@@ -90,6 +90,7 @@
 /*
  * HV_CPUID_NESTED_FEATURES.EAX bits
  */
+#define HV_NESTED_DIRECT_FLUSH              (1u << 17)
 #define HV_NESTED_MSR_BITMAP                (1u << 19)
 
 /*
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 3429a4e455..bb6a5dd498 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6974,6 +6974,8 @@ static Property x86_cpu_properties[] = {
                       HYPERV_FEAT_XMM_INPUT, 0),
     DEFINE_PROP_BIT64("hv-tlbflush-ext", X86CPU, hyperv_features,
                       HYPERV_FEAT_TLBFLUSH_EXT, 0),
+    DEFINE_PROP_BIT64("hv-tlbflush-direct", X86CPU, hyperv_features,
+                      HYPERV_FEAT_TLBFLUSH_DIRECT, 0),
     DEFINE_PROP_ON_OFF_AUTO("hv-no-nonarch-coresharing", X86CPU,
                             hyperv_no_nonarch_cs, ON_OFF_AUTO_OFF),
     DEFINE_PROP_BIT64("hv-syndbg", X86CPU, hyperv_features,
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index a11c8e88f6..f148a6d52f 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -995,6 +995,14 @@ static struct {
         },
         .dependencies = BIT(HYPERV_FEAT_TLBFLUSH)
     },
+    [HYPERV_FEAT_TLBFLUSH_DIRECT] = {
+        .desc = "direct TLB flush (hv-tlbflush-direct)",
+        .flags = {
+            {.func = HV_CPUID_NESTED_FEATURES, .reg = R_EAX,
+             .bits = HV_NESTED_DIRECT_FLUSH}
+        },
+        .dependencies = BIT(HYPERV_FEAT_VAPIC)
+    },
 };
 
 static struct kvm_cpuid2 *try_get_hv_cpuid(CPUState *cs, int max,
-- 
2.36.1