KVM: x86: Initialize tdp_level during vCPU creation

Initialize vcpu->arch.tdp_level during vCPU creation to avoid consuming
garbage if userspace calls KVM_RUN without first calling KVM_SET_CPUID.

Fixes: e93fd3b3 ("KVM: x86/mmu: Capture TDP level when updating CPUID")
Reported-by: syzbot+904752567107eefb728c@syzkaller.appspotmail.com
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200527085400.23759-1-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -9418,6 +9418,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 	fx_init(vcpu);
 
 	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
+	vcpu->arch.tdp_level = kvm_x86_ops.get_tdp_level(vcpu);
 
 	vcpu->arch.pat = MSR_IA32_CR_PAT_DEFAULT;