Re: [edk2-devel] [PATCH V6 33/42] OvmfPkg: Update PlatformInitLib for Tdx guest to publish ram regions

["Yao, Jiewen" <jiewen.yao@intel.com>]

I think both are correct.

The dump info is from a *client* machine in old generation - kabylake. 39 bits physical is good enough.

GPAW in TD is enforced by TDX-module. Please refer to
https://www.intel.com/content/dam/develop/external/us/en/documents/tdx-module-1.0-public-spec-v0.931.pdf, 
Section 10.1.2, Table 10.1 - RBX[5:0] is GPAW - only 48 and 52 are possible.

Thank you
Yao Jiewen

> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Gerd
> Hoffmann
> Sent: Wednesday, February 23, 2022 6:07 PM
> To: Xu, Min M <min.m.xu@intel.com>
> Cc: devel@edk2.groups.io; Ard Biesheuvel <ardb+tianocore@kernel.org>; Justen,
> Jordan L <jordan.l.justen@intel.com>; Brijesh Singh <brijesh.singh@amd.com>;
> Aktas, Erdem <erdemaktas@google.com>; James Bottomley
> <jejb@linux.ibm.com>; Yao, Jiewen <jiewen.yao@intel.com>; Tom Lendacky
> <thomas.lendacky@amd.com>
> Subject: Re: [edk2-devel] [PATCH V6 33/42] OvmfPkg: Update PlatformInitLib
> for Tdx guest to publish ram regions
> 
>   Hi,
> 
> > Another update is in PlatformAddressWidthInitialization. The physical
> > address width that Tdx guest supports is either 48 or 52.
> 
> Hmm.  Sure this is correct?
> 
> 48 is the max _virtual_ address space possible with 4-level paging.
> The _physical_ address space might be much smaller, like this
> (kaby lake desktop system):
> 
>     # lscpu
>     Architecture:            x86_64
>       CPU op-mode(s):        32-bit, 64-bit
>       Address sizes:         39 bits physical, 48 bits virtual
>       Byte Order:            Little Endian
> 
> Maybe all TDX-capable Intel CPUs actually have >= 48 bits physical,
> so this could be fine, but please double-check.
> 
> thanks,
>   Gerd
> 
> 
> 
> 
>