[PATCH v2 3/6] KVM: x86: nSVM: implement nested LBR virtualization

[Maxim Levitsky]

This was tested with kvm-unit-test that was developed
for this purpose.

Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
---
 arch/x86/kvm/svm/nested.c | 21 +++++++++++++++++++--
 arch/x86/kvm/svm/svm.c    |  8 ++++++++
 arch/x86/kvm/svm/svm.h    |  1 +
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 9239631846d88..eca0f2f41bf30 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -518,8 +518,19 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 		vmcb_mark_dirty(svm->vmcb, VMCB_DR);
 	}
 
-	if (unlikely(svm->vmcb01.ptr->control.virt_ext & LBR_CTL_ENABLE_MASK))
+	if (unlikely(svm->lbrv_enabled && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
+		svm_copy_lbrs(vmcb12, svm->vmcb);
+		/*
+		 * TODO: to avoid TOC/TOU race,
+		 * make sure that we only pick LBR enable bit from
+		 * the guest.
+		 */
+		svm->vmcb->save.dbgctl &= LBR_CTL_ENABLE_MASK;
+		svm_update_lbrv(&svm->vcpu);
+
+	} else if (unlikely(svm->vmcb01.ptr->control.virt_ext & LBR_CTL_ENABLE_MASK)) {
 		svm_copy_lbrs(svm->vmcb01.ptr, svm->vmcb);
+	}
 }
 
 static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
@@ -579,6 +590,9 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 
 	svm->vmcb->control.virt_ext            = svm->vmcb01.ptr->control.virt_ext &
 						 LBR_CTL_ENABLE_MASK;
+	if (svm->lbrv_enabled)
+		svm->vmcb->control.virt_ext  |=
+			(svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK);
 
 	nested_svm_transition_tlb_flush(vcpu);
 
@@ -841,7 +855,10 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	svm_switch_vmcb(svm, &svm->vmcb01);
 
-	if (unlikely(svm->vmcb->control.virt_ext & LBR_CTL_ENABLE_MASK)) {
+	if (unlikely(svm->lbrv_enabled && (svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))) {
+		svm_copy_lbrs(svm->nested.vmcb02.ptr, vmcb12);
+		svm_update_lbrv(vcpu);
+	} else if (unlikely(svm->vmcb->control.virt_ext & LBR_CTL_ENABLE_MASK)) {
 		svm_copy_lbrs(svm->nested.vmcb02.ptr, svm->vmcb);
 		svm_update_lbrv(vcpu);
 	}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index c08f8804d107f..0ae8fa9400902 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -884,6 +884,10 @@ void svm_update_lbrv(struct kvm_vcpu *vcpu)
 	bool current_enable_lbrv = !!(svm->vmcb->control.virt_ext &
 				      LBR_CTL_ENABLE_MASK);
 
+	if (unlikely(is_guest_mode(vcpu) && svm->lbrv_enabled))
+		if (unlikely(svm->nested.ctl.virt_ext & LBR_CTL_ENABLE_MASK))
+			enable_lbrv = true;
+
 	if (enable_lbrv == current_enable_lbrv)
 		return;
 
@@ -1016,6 +1020,9 @@ static __init void svm_set_cpu_caps(void)
 		if (tsc_scaling)
 			kvm_cpu_cap_set(X86_FEATURE_TSCRATEMSR);
 
+		if (lbrv)
+			kvm_cpu_cap_set(X86_FEATURE_LBRV);
+
 		/* Nested VM can receive #VMEXIT instead of triggering #GP */
 		kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK);
 	}
@@ -4147,6 +4154,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 			     guest_cpuid_has(vcpu, X86_FEATURE_NRIPS);
 
 	svm->tsc_scaling_enabled = tsc_scaling && guest_cpuid_has(vcpu, X86_FEATURE_TSCRATEMSR);
+	svm->lbrv_enabled = lbrv && guest_cpuid_has(vcpu, X86_FEATURE_LBRV);
 
 	svm_recalc_instruction_intercepts(vcpu, svm);
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index ff84f84f697f7..c3d46fdf4b9ad 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -164,6 +164,7 @@ struct vcpu_svm {
 	/* cached guest cpuid flags for faster access */
 	bool nrips_enabled                : 1;
 	bool tsc_scaling_enabled          : 1;
+	bool lbrv_enabled                 : 1;
 
 	u32 ldr_reg;
 	u32 dfr_reg;
-- 
2.26.3