Re: [PATCH v2 03/17] x86/virt/tdx: Detect if the extensions initialization is required

[Edgecombe, Rick P]

On Wed, 2026-07-29 at 11:50 +0800, Xu Yilun wrote:
> On Mon, Jul 27, 2026 at 05:56:31PM +0000, Edgecombe, Rick P wrote:
> > On Mon, 2026-07-27 at 20:38 +0800, Xu Yilun wrote:
> > > > This is not true. There are some normal (non-extension) SEAMCALLs also
> > > > are
> > > > preemptible and resumable. For example,
> > > > 
> > > > - TDH.PHYMEM.CACHE.WB
> > > > - TDH.SYS.DISABLE
> > > > - TDH.MEM.SEPT.ADD with version 1
> > > 
> > > No they are not preemptible and resumable. They just intentionally
> > > yield and don't have a generic way to save/resume their context. You
> > > can't rely on that to implement complex tasks in TDX module considering
> > > the complexity. That's the main reason why TDX module extensions are
> > > needed.
> > 
> > We have RESUMABLE seamcalls today. They are guaranteed to save state and
> > make
> > forward progress. Xiaoyao is right, this is not a new concept from the VMM
> > side.
> 
> OK. Let me de-emphasize resumable.
> 
> And I'm thinking of how to stop explaining new terms again and again,
> extension SEAMCALL is the one. I'm not sure if calling it "preemptible
> SEAMCALLs" helps, or is it still a new term?
> 
> > But also why highlight this for the patch here. Are you trying to explain
> > why
> > extension initialization needs some special step?
> 
> I was following the suggestion [1] of explaining the context in general.
> But yes, a brief explaination of why we need special initialization is
> good to me: A global service environment should be built to provide
> some general context switching mechanism inside TDX module.

Wait are all extension seamcalls resumable? Couldn't there be one associated
with an extension that is not? We have so far explained extensions in terms of
the TDX module needing more memory for the optional features. So "extension"
probably be interpreted as "optional", not as enabling "preemptible" seamcalls.

> 
> [1]:
> https://lore.kernel.org/all/1783e7bd-3759-41f7-93e3-2f9e21264bd4@xxxxxxxxx/
> 
> Refactored the first paragraph:
> 
> ----8<----
> 
>   TDX adds a new class of SEAMCALLs which are preemptible and can cooperate
>   with the host scheduling. 

But these are not new is the point. Look for TDX_INTERRUPTED_RESUMABLE in Linux
and TDX source.

> Some features like TDISP, DICE-based quoting
>   rely on these preemptible SEAMCALLs to implement higher order security
>   protocols with simple ABIs. To enable preemptible SEAMCALLs, a global
>   service environment, called TDX module extensions, must first be
>   initialized.

Why are we even talking about this in a patch that reads the metadata. Is it
necessary?

> 
>   ...