I've discussed that here, here and here.
In Microsoft's announcement of their patches for Meltdown and Spectre they included the following:
Note: Customers will not receive the January 2018 security updates (or any subsequent security updates) and will not be protected from security vulnerabilities unless their antivirus software vendor sets the following registry key:Read that again.
If your anti-virus vendor doesn't set a new registry key you will NEVER get another security update.
Now, certainly mainstream anti-virus vendors quickly complied.
But what that means is that mainstream anti-virus vendors have been using non-public kernel calls.
Don't do that.
Further if you don't run any anti-virus you must manually set that registry key or you will NEVER get another security update.
In cases where customers can’t install or run antivirus software, Microsoft recommends manually setting the registry key as described below in order to receive the January 2018 security updates.There's a pertinent blog post here.