[RFC PATCH v1 3/4] KVM: x86: nSVM: Implement support for nested Bus Lock Threshold

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

Expose the Bus Lock Threshold in the guest CPUID and support its
functionality in nested guest.

Ensure proper restoration and saving of the bus_lock_counter at VM
Entry and VM Exit respectively in nested guest scenarios.

Case 1:
L0 supports buslock exit and L1 does not: use buslock counter from L0
and exits happen to L0 VMM.

Case 2:
Both L0 and L1 supports buslock exit: use L1 buslock counter value and
exits happen to L1 VMM.

Signed-off-by: Manali Shukla <manali.shukla@amd.com>
---
 arch/x86/kvm/governed_features.h |  1 +
 arch/x86/kvm/svm/nested.c        | 25 +++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.c           |  5 +++++
 arch/x86/kvm/svm/svm.h           |  1 +
 4 files changed, 32 insertions(+)

diff --git a/arch/x86/kvm/governed_features.h b/arch/x86/kvm/governed_features.h
index ad463b1ed4e4..0982eb107f0b 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(BUS_LOCK_THRESHOLD)
 
 #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 6f704c1037e5..d09434225e4d 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -363,6 +363,7 @@ void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
 	to->virt_ext            = from->virt_ext;
 	to->pause_filter_count  = from->pause_filter_count;
 	to->pause_filter_thresh = from->pause_filter_thresh;
+	to->bus_lock_counter    = from->bus_lock_counter;
 
 	/* Copy asid here because nested_vmcb_check_controls will check it.  */
 	to->asid           = from->asid;
@@ -758,6 +759,16 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
 		}
 	}
 
+	/*
+	 * If guest intercepts BUSLOCK, use guest's bus_lock_counter value,
+	 * otherwise use host bus_lock_counter value.
+	 */
+	if (guest_can_use(vcpu, X86_FEATURE_BUS_LOCK_THRESHOLD) &&
+	    vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_BUSLOCK))
+		vmcb02->control.bus_lock_counter = svm->nested.ctl.bus_lock_counter;
+	else
+		vmcb02->control.bus_lock_counter = vmcb01->control.bus_lock_counter;
+
 	nested_svm_transition_tlb_flush(vcpu);
 
 	/* Enter Guest-Mode */
@@ -1035,6 +1046,12 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	}
 
+	if (guest_can_use(vcpu, X86_FEATURE_BUS_LOCK_THRESHOLD) &&
+	    vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_BUSLOCK))
+		vmcb12->control.bus_lock_counter = vmcb02->control.bus_lock_counter;
+	else
+		vmcb01->control.bus_lock_counter = vmcb02->control.bus_lock_counter;
+
 	nested_svm_copy_common_state(svm->nested.vmcb02.ptr, svm->vmcb01.ptr);
 
 	svm_switch_vmcb(svm, &svm->vmcb01);
@@ -1333,6 +1350,13 @@ static int nested_svm_intercept(struct vcpu_svm *svm)
 		vmexit = NESTED_EXIT_DONE;
 		break;
 	}
+	case SVM_EXIT_BUS_LOCK: {
+		if (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_BUSLOCK)))
+			vmexit = NESTED_EXIT_HOST;
+		else
+			vmexit = NESTED_EXIT_DONE;
+		break;
+	}
 	default: {
 		if (vmcb12_is_intercept(&svm->nested.ctl, exit_code))
 			vmexit = NESTED_EXIT_DONE;
@@ -1572,6 +1596,7 @@ static void nested_copy_vmcb_cache_to_control(struct vmcb_control_area *dst,
 	dst->virt_ext              = from->virt_ext;
 	dst->pause_filter_count   = from->pause_filter_count;
 	dst->pause_filter_thresh  = from->pause_filter_thresh;
+	dst->bus_lock_counter     = from->bus_lock_counter;
 	/* 'clean' and 'hv_enlightenments' are not changed by KVM */
 }
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 9f1d51384eac..bb2437a7694c 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4373,6 +4373,8 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_FLUSH_CMD, 0,
 				     !!guest_cpuid_has(vcpu, X86_FEATURE_FLUSH_L1D));
 
+	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_BUS_LOCK_THRESHOLD);
+
 	if (cpu_feature_enabled(X86_FEATURE_BUS_LOCK_THRESHOLD) &&
 	    vcpu->kvm->arch.bus_lock_detection_enabled) {
 		svm_set_intercept(svm, INTERCEPT_BUSLOCK);
@@ -5183,6 +5185,9 @@ static __init void svm_set_cpu_caps(void)
 		if (vnmi)
 			kvm_cpu_cap_set(X86_FEATURE_VNMI);
 
+		if (cpu_feature_enabled(X86_FEATURE_BUS_LOCK_THRESHOLD))
+			kvm_cpu_cap_set(X86_FEATURE_BUS_LOCK_THRESHOLD);
+
 		/* Nested VM can receive #VMEXIT instead of triggering #GP */
 		kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK);
 	}
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 8983eabf8f84..f49ea38187ba 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -150,6 +150,7 @@ struct vmcb_ctrl_area_cached {
 	u64 nested_cr3;
 	u64 virt_ext;
 	u32 clean;
+	u16 bus_lock_counter;
 	union {
 #if IS_ENABLED(CONFIG_HYPERV) || IS_ENABLED(CONFIG_KVM_HYPERV)
 		struct hv_vmcb_enlightenments hv_enlightenments;
-- 
2.34.1