On Mon, Sep 26, 2022, Paolo Bonzini wrote: > 32-bit KVM has extra complications in the code due to: > > - different ways to write 64-bit values in VMCS > > - different handling of DS and ES selectors as well as FS/GS bases > > - lack of CR8 and EFER > > - lack of XFD > More for the list: - SVM is effectively restricted to PAE kernels due to NX requirements > - impossibility of writing 64-bit PTEs atomically It's not impossible, just ugly. KVM could use CMPXCHG8B to do all of the accesses for the TDP MMU, including the non-atomic reads and writes. > The last is the big one, because it prevents from using the TDP MMU > unconditionally. As above, if the TDP MMU really is the sticking point, that's solvable. The real justification for deprecating 32-bit KVM is that, outside of KVM developers, literally no one uses 32-bit KVM. I.e. any amount of effort that is required to continue supporting 32-bit kernels is a complete waste of resources.
