Re: [edk2-devel] [PATCH V5 2/2] OvmfPkg/ResetVector: Enable Intel TDX in ResetVector of Ovmf

["Gerd Hoffmann" <kraxel@redhat.com>]

  Hi,

> > If we can use 4-level paging initially, then we surely should go for option (1)
> > and simply not touch the reset vectors paging code.

> After PoC I find this option is not a good one. Though the reset
> vectors is not touched, there are tricky changes in DxeIpl. To set up
> 5-level paging in an 4-level paging, it should first be switched from
> 64-bit long mode to 32 protected mode, then turn off the Paging,
> disable IA32_ERER.LME, then set the Cr4. The tricky thing is that in
> TDX IA32_EFER is not changeable. MdeModulePkg/.../DxeIpl is widely
> used and  it is high risk to make such changes.

Ok.  One more question:  Do we have to use 5-level paging at all?

The only reason I could see is accepting memory with a gpa above 4-level
address space.  But with the longer-term plan to support lazy acceptance
(and passing unaccepted memory ranges to the guest kernel) this reason
goes away.

So I think we could just leave it to the guest kernel to deal with the
switch from 4-level to 5-level paging.  Or do I miss something?

take care,
  Gerd