KVM: x86/mmu: Don't do TLB flush when zappings SPTEs in invalid roots

Don't force a TLB flush when zapping SPTEs in invalid roots as vCPUs
can't be actively using invalid roots (zapping SPTEs in invalid roots is
necessary only to ensure KVM doesn't mark a page accessed/dirty after it
is freed by the primary MMU).

Link: https://lore.kernel.org/r/20240111020048.844847-3-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/mmu/tdp_mmu.c

@@ -811,7 +811,13 @@ static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,
 			continue;
 
 		tdp_mmu_iter_set_spte(kvm, &iter, 0);
-		flush = true;
+
+		/*
+		 * Zappings SPTEs in invalid roots doesn't require a TLB flush,
+		 * see kvm_tdp_mmu_zap_invalidated_roots() for details.
+		 */
+		if (!root->role.invalid)
+			flush = true;
 	}
 
 	rcu_read_unlock();