Yes, we are aware of IBM's lack of information on that page. We are disclosing some of the details of the issue to keep our security-conscious customers informed.

In a nutshell, only the DD2.2 silicon changes were needed. DD2.2 silicon is able to close off these security holes, with the exception of the Spectre same-process read vulnerability that affects the entire CPU industry, with only changes to firmware and a small kernel change. Note that the kernel change is minimally invasive and is not related to the 30% performance loss Intel KPTI mitigation.