KVM: X86: Skip allocating pae_root for vcpu->arch.guest_mmu when !tdp_enabled

It is never used.
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211118110814.2568-11-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -5514,6 +5514,10 @@ static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
 	for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++)
 		mmu->prev_roots[i] = KVM_MMU_ROOT_INFO_INVALID;
 
+	/* vcpu->arch.guest_mmu isn't used when !tdp_enabled. */
+	if (!tdp_enabled && mmu == &vcpu->arch.guest_mmu)
+		return 0;
+
 	/*
 	 * When using PAE paging, the four PDPTEs are treated as 'root' pages,
 	 * while the PDP table is a per-vCPU construct that's allocated at MMU