Re: [PATCH 18/25] KVM: TDX: Do TDX specific vcpu initialization

[Edgecombe, Rick P]

On Mon, 2024-10-21 at 16:35 +0800, Xiaoyao Li wrote:
> > 
> > How about adding it to the docs?
> 
> OK for me.

Can you propose something?

> 
> > > 
> > > It's architectural valid that userspace VMM creates a TD with legacy
> > > topology, i.e., topology enumerated via CPUID 0x1 and 0x4.
> > > 
> > > > In that case, do you see a need for the vanilla tdh_vp_init() SEAMCALL
> > > > wrapper?
> > > > 
> > > > The TDX module version we need already supports enum_topology, so the
> > > > code:
> > > >    	if (modinfo->tdx_features0 &
> > > > MD_FIELD_ID_FEATURES0_TOPOLOGY_ENUM)
> > > >    		err = tdh_vp_init_apicid(tdx, vcpu_rcx, vcpu->vcpu_id);
> > > >    	else
> > > >    		err = tdh_vp_init(tdx, vcpu_rcx);
> > > > 
> > > > The tdh_vp_init() branch shouldn't be hit.
> > > 
> > > We cannot know what version of TDX module user might use thus we cannot
> > > assume enum_topology is always there unless we make it a hard
> > > requirement in KVM that TDX fails being enabled when
> > > 
> > >      !(modinfo->tdx_features0 & MD_FIELD_ID_FEATURES0_TOPOLOGY_ENUM)
> > 
> > We will depend on bugs that are fixed in TDX Modules after enum topology, so
> > it
> > shouldn't be required in the normal case. So I think it would be simpler to
> > add
> > this tdx_features0 conditional. We can then export one less SEAMCALL and
> > will
> > have less configurations flows to worry about on the KVM side.
> 
> I'm a little bit confused. what does "add this tdx_feature0 conditional" 
> mean?

I was talking about your suggestion to check for
MD_FIELD_ID_FEATURES0_TOPOLOGY_ENUM.