[PATCH v4 3/4] KVM: nSVM: implement the nested idle halt intercept

[Manali Shukla <manali.shukla@amd.com>]

Enable the idle HLT intercept for the L2 guest when it is available on
the platform and the L2 guest can utilize the Idle HLT intercept
feature. This is achieved by clearing the HLT intercept for the L1
hypervisor in the recalc_interrupts() function. The Idle HLT intercept
requires that the HLT intercept is cleared and the Idle HLT intercept
is set to properly enable the feature.

The nested idle halt intercept was tested by booting L1,L2 (all Linux)
and checking there are only idle-hlt vmexits happened.

Signed-off-by: Manali Shukla <manali.shukla@amd.com>
---
 arch/x86/kvm/governed_features.h | 1 +
 arch/x86/kvm/svm/nested.c        | 8 ++++++++
 arch/x86/kvm/svm/svm.c           | 4 ++++
 3 files changed, 13 insertions(+)

diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
index ad463b1ed4e4..0154012721cb 100644
--- a/arch/x86/kvm/governed_features.h
+++ b/arch/x86/kvm/governed_features.h
@@ -17,6 +17,7 @@ KVM_GOVERNED_X86_FEATURE(PFTHRESHOLD)
 KVM_GOVERNED_X86_FEATURE(VGIF)
 KVM_GOVERNED_X86_FEATURE(VNMI)
 KVM_GOVERNED_X86_FEATURE(LAM)
+KVM_GOVERNED_X86_FEATURE(IDLE_HLT)
 
 #undef KVM_GOVERNED_X86_FEATURE
 #undef KVM_GOVERNED_FEATURE
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index d5314cb7dff4..feb241110f1a 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -178,6 +178,14 @@ void recalc_intercepts(struct vcpu_svm *svm)
 	} else {
 		WARN_ON(!(c->virt_ext & VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK));
 	}
+
+	/*
+	 * Clear the HLT intercept for L2 guest when the Idle HLT intercept feature
+	 * is enabled on the platform and the guest can use the Idle HLT intercept
+	 * feature.
+	 */
+	if (guest_can_use(&svm->vcpu, X86_FEATURE_IDLE_HLT))
+		vmcb_clr_intercept(c, INTERCEPT_HLT);
 }
 
 /*
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e86b79e975d3..38d546788fc6 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4425,6 +4425,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_PFTHRESHOLD);
 	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_VGIF);
 	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_VNMI);
+	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_IDLE_HLT);
 
 	svm_recalc_instruction_intercepts(vcpu, svm);
 
@@ -5228,6 +5229,9 @@ static __init void svm_set_cpu_caps(void)
 		if (vnmi)
 			kvm_cpu_cap_set(X86_FEATURE_VNMI);
 
+		if (cpu_feature_enabled(X86_FEATURE_IDLE_HLT))
+			kvm_cpu_cap_set(X86_FEATURE_IDLE_HLT);
+
 		/* Nested VM can receive #VMEXIT instead of triggering #GP */
 		kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK);
 	}
-- 
2.34.1