[PATCH RFC 14/19] KVM: x86: hyper-v: Introduce fast kvm_hv_direct_tlb_flush_exposed() check

[Vitaly Kuznetsov]

Introduce a helper to quickly check if KVM needs to handle VMCALL/VMMCALL
from L2 in L0 to process Direct TLB flush requests.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/hyperv.c           | 6 ++++++
 arch/x86/kvm/hyperv.h           | 7 +++++++
 3 files changed, 14 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 45ee05f4f1a0..bcaf05951628 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -611,6 +611,7 @@ struct kvm_vcpu_hv {
 		u32 enlightenments_eax; /* HYPERV_CPUID_ENLIGHTMENT_INFO.EAX */
 		u32 enlightenments_ebx; /* HYPERV_CPUID_ENLIGHTMENT_INFO.EBX */
 		u32 syndbg_cap_eax; /* HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES.EAX */
+		u32 nested_features_eax; /* HYPERV_CPUID_NESTED_FEATURES.EAX */
 	} cpuid_cache;
 
 	/* Two rings for regular Hyper-V TLB flush and Direct TLB flush */
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 865b4d9a26fe..31acc08a6b23 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2270,6 +2270,12 @@ void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu)
 		hv_vcpu->cpuid_cache.syndbg_cap_eax = entry->eax;
 	else
 		hv_vcpu->cpuid_cache.syndbg_cap_eax = 0;
+
+	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_NESTED_FEATURES, 0);
+	if (entry)
+		hv_vcpu->cpuid_cache.nested_features_eax = entry->eax;
+	else
+		hv_vcpu->cpuid_cache.nested_features_eax = 0;
 }
 
 int kvm_hv_set_enforce_cpuid(struct kvm_vcpu *vcpu, bool enforce)
diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
index 0c0877a6aa74..0c9062aed182 100644
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -169,6 +169,13 @@ static inline void kvm_hv_vcpu_empty_flush_tlb(struct kvm_vcpu *vcpu)
 	tlb_flush_ring->read_idx = tlb_flush_ring->write_idx;
 }
 
+static inline bool kvm_hv_direct_tlb_flush_exposed(struct kvm_vcpu *vcpu)
+{
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+	return hv_vcpu && (hv_vcpu->cpuid_cache.nested_features_eax & HV_X64_NESTED_DIRECT_FLUSH);
+}
+
 static inline bool kvm_hv_is_tlb_flush_hcall(struct kvm_vcpu *vcpu)
 {
 	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
-- 
2.35.1