KVM: nSVM: leave guest mode when clearing EFER.SVME

According to the AMD manual, the effect of turning off EFER.SVME while a
guest is running is undefined.  We make it leave guest mode immediately,
similar to the effect of clearing the VMX bit in MSR_IA32_FEAT_CTL.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/nested.c

@@ -618,6 +618,22 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	return 0;
 }
 
+/*
+ * Forcibly leave nested mode in order to be able to reset the VCPU later on.
+ */
+void svm_leave_nested(struct vcpu_svm *svm)
+{
+	if (is_guest_mode(&svm->vcpu)) {
+		struct vmcb *hsave = svm->nested.hsave;
+		struct vmcb *vmcb = svm->vmcb;
+
+		svm->nested.nested_run_pending = 0;
+		leave_guest_mode(&svm->vcpu);
+		copy_vmcb_control_area(&vmcb->control, &hsave->control);
+		nested_svm_uninit_mmu_context(&svm->vcpu);
+	}
+}
+
 static int nested_svm_exit_handled_msr(struct vcpu_svm *svm)
 {
 	u32 offset, msr, value;

arch/x86/kvm/svm/svm.c

@@ -265,6 +265,7 @@ static int get_npt_level(struct kvm_vcpu *vcpu)
 
 void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 {
+	struct vcpu_svm *svm = to_svm(vcpu);
 	vcpu->arch.efer = efer;
 
 	if (!npt_enabled) {
@@ -275,8 +276,13 @@ void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 			efer &= ~EFER_LME;
 	}
 
-	to_svm(vcpu)->vmcb->save.efer = efer | EFER_SVME;
+	if (!(efer & EFER_SVME)) {
-	mark_dirty(to_svm(vcpu)->vmcb, VMCB_CR);
+		svm_leave_nested(svm);
+		svm_set_gif(svm, true);
+	}
+
+	svm->vmcb->save.efer = efer | EFER_SVME;
+	mark_dirty(svm->vmcb, VMCB_CR);
 }
 
 static int is_external_interrupt(u32 info)

arch/x86/kvm/svm/svm.h

@@ -389,6 +389,7 @@ static inline bool nested_exit_on_nmi(struct vcpu_svm *svm)
 
 void enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
 			  struct vmcb *nested_vmcb);
+void svm_leave_nested(struct vcpu_svm *svm);
 int nested_svm_vmrun(struct vcpu_svm *svm);
 void nested_svm_vmloadsave(struct vmcb *from_vmcb, struct vmcb *to_vmcb);
 int nested_svm_vmexit(struct vcpu_svm *svm);