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

[Min Xu]

On Monday, August 30, 2021 3:41 PM, Gerd Hoffmann wrote:
>   Hi,
> 
> >  _TdxPageTable:
> >     If 5-level page table is supported (GPAW is 52), a top level page
> >     directory pointers (1 * 256TB entry) is generated in this page.
> >  _OvmfPageTable:
> >     Initial page table for standard Ovmf.
> 
> Hmm, isn't 5-level paging independent from TDX?  Why mix the two?
> 
> I think a top level page directory should be added to the standard ovmf initial
> page tables instead, and setting up 5-level paging should not happen in tdx-
> specific code.
In current Ovmf implementation (OvmfPkg/ResetVector/Ia32/PageTables64.asm)
there are 6 pages reserved for initial page tables. It doesn't support 5-level paging.

TDX support GPAW 48 and 52. If GPAW is 52 we need an extra page to hold the top
level page directory pointers (1 * 256TB entry).

This TDX extra page reuses the memory region defined by PcdOvmfSecGhcbPageTableBase
In MEMFD. Because this memory region (PcdOvmfSecGhcbPageTableBase) will not
be consumed by SEV code in Tdx guest.
> 
Thanks!
Min


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