On Tue, 2024-05-07 at 22:22 +0800, Chao Gao wrote: > > 2. There was some concern that exposing non-zero bits in [23:16] could > > confuse > > existing TDs. Of course KVM doesn't support any TDs today, but if this > > feature > > comes after initial KVM support for TDX and KVM wants to set it by default, > > then > > it could be an issue. > > Do you mean some TDs may assert that [23:16] are 0s? A future-proof design > won't have this assertion. And this case (i.e., some CPUID bits become non- > zero) > happens on every new generation of CPUs and doesn't confuse existing OSes. I > don't understand why it would be a problem for TDs. Intel defined these as reserved. AMD defined them for guest MAXPA. So, yes, OSs should be masking them. I'm not suggesting that any are not, but TDX module folks were concerned about this, and that then KVM would not be able to turn this on later without breaking them. So just circling back here to double check.
