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 <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

1 files changed, 79 insertions, 19 deletions

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index c39f2655ceeb..699a367af107 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/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:
 		/*