KVM: SVM: Sync efer back into nested vmcb

This patch fixes a bug in a nested hypervisor that heavily
switches between real-mode and long-mode. The problem is
fixed by syncing back efer into the guest vmcb on emulated
vmexit.
Signed-off-by: NJoerg Roedel <joerg.roedel@amd.com>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/svm.c

@@ -1896,6 +1896,7 @@ static int nested_svm_vmexit(struct vcpu_svm *svm)
 	nested_vmcb->save.ds     = vmcb->save.ds;
 	nested_vmcb->save.gdtr   = vmcb->save.gdtr;
 	nested_vmcb->save.idtr   = vmcb->save.idtr;
+	nested_vmcb->save.efer   = svm->vcpu.arch.efer;
 	nested_vmcb->save.cr0    = kvm_read_cr0(&svm->vcpu);
 	nested_vmcb->save.cr3    = svm->vcpu.arch.cr3;
 	nested_vmcb->save.cr2    = vmcb->save.cr2;