KVM: x86: nSVM: correctly virtualize LBR msrs when L2 is running

When L2 is running without LBR virtualization, we should ensure
that L1's LBR msrs continue to update as usual.
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220322174050.241850-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/nested.c

@@ -536,6 +536,7 @@ void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm)
 static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12)
 {
 	bool new_vmcb12 = false;
+	struct vmcb *vmcb01 = svm->vmcb01.ptr;
 	struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
 
 	nested_vmcb02_compute_g_pat(svm);
@@ -586,6 +587,9 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 		svm->vcpu.arch.dr6  = svm->nested.save.dr6 | DR6_ACTIVE_LOW;
 		vmcb_mark_dirty(vmcb02, VMCB_DR);
 	}
+
+	if (unlikely(vmcb01->control.virt_ext & LBR_CTL_ENABLE_MASK))
+		svm_copy_lbrs(vmcb02, vmcb01);
 }
 
 static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
@@ -645,6 +649,9 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 	vmcb02->control.event_inj           = svm->nested.ctl.event_inj;
 	vmcb02->control.event_inj_err       = svm->nested.ctl.event_inj_err;
 
+	vmcb02->control.virt_ext            = vmcb01->control.virt_ext &
+					      LBR_CTL_ENABLE_MASK;
+
 	if (!nested_vmcb_needs_vls_intercept(svm))
 		vmcb02->control.virt_ext |= VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
 
@@ -912,6 +919,11 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	svm_switch_vmcb(svm, &svm->vmcb01);
 
+	if (unlikely(vmcb01->control.virt_ext & LBR_CTL_ENABLE_MASK)) {
+		svm_copy_lbrs(vmcb01, vmcb02);
+		svm_update_lbrv(vcpu);
+	}
+
 	/*
 	 * On vmexit the  GIF is set to false and
 	 * no event can be injected in L1.

arch/x86/kvm/svm/svm.c

@@ -793,6 +793,17 @@ static void init_msrpm_offsets(void)
 	}
 }
 
+void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
+{
+	to_vmcb->save.dbgctl		= from_vmcb->save.dbgctl;
+	to_vmcb->save.br_from		= from_vmcb->save.br_from;
+	to_vmcb->save.br_to		= from_vmcb->save.br_to;
+	to_vmcb->save.last_excp_from	= from_vmcb->save.last_excp_from;
+	to_vmcb->save.last_excp_to	= from_vmcb->save.last_excp_to;
+
+	vmcb_mark_dirty(to_vmcb, VMCB_LBR);
+}
+
 static void svm_enable_lbrv(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -802,6 +813,10 @@ static void svm_enable_lbrv(struct kvm_vcpu *vcpu)
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTBRANCHTOIP, 1, 1);
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTFROMIP, 1, 1);
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTTOIP, 1, 1);
+
+	/* Move the LBR msrs to the vmcb02 so that the guest can see them. */
+	if (is_guest_mode(vcpu))
+		svm_copy_lbrs(svm->vmcb, svm->vmcb01.ptr);
 }
 
 static void svm_disable_lbrv(struct kvm_vcpu *vcpu)
@@ -813,6 +828,63 @@ static void svm_disable_lbrv(struct kvm_vcpu *vcpu)
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTBRANCHTOIP, 0, 0);
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTFROMIP, 0, 0);
 	set_msr_interception(vcpu, svm->msrpm, MSR_IA32_LASTINTTOIP, 0, 0);
+
+	/*
+	 * Move the LBR msrs back to the vmcb01 to avoid copying them
+	 * on nested guest entries.
+	 */
+	if (is_guest_mode(vcpu))
+		svm_copy_lbrs(svm->vmcb01.ptr, svm->vmcb);
+}
+
+static int svm_get_lbr_msr(struct vcpu_svm *svm, u32 index)
+{
+	/*
+	 * If the LBR virtualization is disabled, the LBR msrs are always
+	 * kept in the vmcb01 to avoid copying them on nested guest entries.
+	 *
+	 * If nested, and the LBR virtualization is enabled/disabled, the msrs
+	 * are moved between the vmcb01 and vmcb02 as needed.
+	 */
+	struct vmcb *vmcb =
+		(svm->vmcb->control.virt_ext & LBR_CTL_ENABLE_MASK) ?
+			svm->vmcb : svm->vmcb01.ptr;
+
+	switch (index) {
+	case MSR_IA32_DEBUGCTLMSR:
+		return vmcb->save.dbgctl;
+	case MSR_IA32_LASTBRANCHFROMIP:
+		return vmcb->save.br_from;
+	case MSR_IA32_LASTBRANCHTOIP:
+		return vmcb->save.br_to;
+	case MSR_IA32_LASTINTFROMIP:
+		return vmcb->save.last_excp_from;
+	case MSR_IA32_LASTINTTOIP:
+		return vmcb->save.last_excp_to;
+	default:
+		KVM_BUG(false, svm->vcpu.kvm,
+			"%s: Unknown MSR 0x%x", __func__, index);
+		return 0;
+	}
+}
+
+void svm_update_lbrv(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	bool enable_lbrv = svm_get_lbr_msr(svm, MSR_IA32_DEBUGCTLMSR) &
+					   DEBUGCTLMSR_LBR;
+
+	bool current_enable_lbrv = !!(svm->vmcb->control.virt_ext &
+				      LBR_CTL_ENABLE_MASK);
+
+	if (enable_lbrv == current_enable_lbrv)
+		return;
+
+	if (enable_lbrv)
+		svm_enable_lbrv(vcpu);
+	else
+		svm_disable_lbrv(vcpu);
 }
 
 void disable_nmi_singlestep(struct vcpu_svm *svm)
@@ -2581,25 +2653,12 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_TSC_AUX:
 		msr_info->data = svm->tsc_aux;
 		break;
-	/*
-	 * Nobody will change the following 5 values in the VMCB so we can
-	 * safely return them on rdmsr. They will always be 0 until LBRV is
-	 * implemented.
-	 */
 	case MSR_IA32_DEBUGCTLMSR:
-		msr_info->data = svm->vmcb->save.dbgctl;
-		break;
 	case MSR_IA32_LASTBRANCHFROMIP:
-		msr_info->data = svm->vmcb->save.br_from;
-		break;
 	case MSR_IA32_LASTBRANCHTOIP:
-		msr_info->data = svm->vmcb->save.br_to;
-		break;
 	case MSR_IA32_LASTINTFROMIP:
-		msr_info->data = svm->vmcb->save.last_excp_from;
-		break;
 	case MSR_IA32_LASTINTTOIP:
-		msr_info->data = svm->vmcb->save.last_excp_to;
+		msr_info->data = svm_get_lbr_msr(svm, msr_info->index);
 		break;
 	case MSR_VM_HSAVE_PA:
 		msr_info->data = svm->nested.hsave_msr;
@@ -2845,12 +2904,13 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		if (data & DEBUGCTL_RESERVED_BITS)
 			return 1;
 
-		svm->vmcb->save.dbgctl = data;
-		vmcb_mark_dirty(svm->vmcb, VMCB_LBR);
-		if (data & (1ULL<<0))
-			svm_enable_lbrv(vcpu);
+		if (svm->vmcb->control.virt_ext & LBR_CTL_ENABLE_MASK)
+			svm->vmcb->save.dbgctl = data;
 		else
-			svm_disable_lbrv(vcpu);
+			svm->vmcb01.ptr->save.dbgctl = data;
+
+		svm_update_lbrv(vcpu);
+
 		break;
 	case MSR_VM_HSAVE_PA:
 		/*

arch/x86/kvm/svm/svm.h

@@ -492,6 +492,8 @@ u32 svm_msrpm_offset(u32 msr);
 u32 *svm_vcpu_alloc_msrpm(void);
 void svm_vcpu_init_msrpm(struct kvm_vcpu *vcpu, u32 *msrpm);
 void svm_vcpu_free_msrpm(u32 *msrpm);
+void svm_copy_lbrs(struct vmcb *to_vmcb, struct vmcb *from_vmcb);
+void svm_update_lbrv(struct kvm_vcpu *vcpu);
 
 int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer);
 void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);