On Tue, Aug 13, 2024, Rick P Edgecombe wrote: > On Tue, 2024-08-13 at 19:34 +0800, Chao Gao wrote: > > Mandating that all fixed-1 bits be supported by KVM would be a burden for both > > KVM and the TDX module: the TDX module couldn't add any fixed-1 bits until KVM > > supports them, and > > > KVM shouldn't drop any feature that was ever a fixed-1 bit > > in any TDX module. > > Honest question...can/does this happen for normal VMs? KVM dropping support for > features? Almost never. KVM still supports Intel CPUs without virtual NMI support, which IIRC was something like one SKU of Yonah that was 32-bit only. Keeping backwards compability is annoying from time to time, but it's generally not that much of a maintenance burden. The only CPUs I really wish had never existed are those that have EPT without A/D bits. Other than that, maintaining support for old CPUs doesn't hinder us too much. > I think I recall even MPX getting limped along for backward compatibility reasons. Yep, KVM still supports virtualizing MPX.
