Re: [PATCH V7 1/1] OvmfPkg: Enable TDX in ResetVector

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

On Thu, Sep 23, 2021 at 12:38:24AM +0000, Xu, Min M wrote:
> On September 22, 2021 3:49 PM, Gerd Hoffmann wrote:
> >   Hi,
> > 
> > > +%ifdef ARCH_X64
> > > +;
> > > +; TDX Metadata offset block
> > > +;
> > > +; TdxMetadata.asm is included in ARCH_X64 because Inte TDX is only ;
> > > +available in ARCH_X64. Below block describes the offset of ;
> > > +TdxMetadata block in Ovmf image ; ; GUID :
> > > +e47a6535-984a-4798-865e-4685a7bf8ec2
> > > +;
> > > +tdxMetadataOffsetStart:
> > > +    DD      tdxMetadataOffsetStart - TdxMetadataGuid - 16
> > > +    DW      tdxMetadataOffsetEnd - tdxMetadataOffsetStart
> > > +    DB      0x35, 0x65, 0x7a, 0xe4, 0x4a, 0x98, 0x98, 0x47
> > > +    DB      0x86, 0x5e, 0x46, 0x85, 0xa7, 0xbf, 0x8e, 0xc2
> > > +tdxMetadataOffsetEnd:
> > > +
> > > +%endif
> > 
> > This should be switched to common ovmf metadata (see patches 4-7 of the
> > SEV-SNP series).
> > 
> > Min: please have a look at these patches.
> >

> Hi, Gerd
> I checked the patches 4-7 of the SEV-SNP series. The common
> OvmfMetadata is designed for both SEV and TDX, right? 

That is the idea, yes.

> If so, then it means the SEV and TDX metadata will be mixed in this
> OvmfMetadata.

Yes.

> I am thinking there will always be different fields for
> SEV and TDX. For example, SEV has PcdOvmfSecGhcbPageTable but TDX
> doesn't need that page. If the common OvmfMetadata is consumed by
> TDX-QEMU, then PcdOvmfSecGhcbPageTableBase will be initialized too.
> That doesn't make sense.

We have different range types.  OVMF_* are the common areas.  SEV_* will
be used by sev only, TDX_* will be used by tdx only.  TDX and SEV
entries are allowed to overlap, i.e. PcdOvmfSecGhcbPageTableBase should
have some SEV_* type for sev (I think this needs fixing in the series),
and tdx can use the page for something else by adding an TDX_* entry for
the same range.

> I am thinking that SEV and TDX can keep their own Metadata (in
> separate files, SevMetadata.asm and TdxMetadata.asm) which are pointed
> by the SEV or TDX offsets in the GUID-ed chain in ResetVector.

I'd very much prefer to have a single table to avoid duplication for the
common memory areas and keep the reset vector small.

Having separate SevMetadata.asm + TdxMetadata.asm files (then have
OvmfMetadata.asm include these two) is an option.  I think this isn't
needed, we can also just group the entries in OvmfMetadata.asm.

> In this case, SEV and TDX can design their own metadata flexibly, for
> example, the attribute, the item structure, add/remove/update the
> items, etc.

Why have two ways to do the same thing?

take care,
  Gerd