Re: [PATCH v3 24/26] x86/virt/seamldr: Extend sigstruct to 16KB

[Huang, Kai]

On Fri, 2026-01-30 at 22:25 +0800, Gao, Chao wrote:
> > Let's move the discussion here (from patch 13 -- sorry about that):
> > 
> > IIRC this patch just simply re-purposes couple of reserved space in
> > SEAMLDR_PARAMS (which is part of P-SEAMLDR ABI) w/o enumeration, explicit
> > opt-in whatever.  The code change here doesn't even bump up its version.
> > 
> > IIUC, if this code run on an old platform where SEAMLDR.INSTALL still only
> > works with 4K SIGSTRUCT, the SEAMLDR.INSTALL will only see part of the
> > SIGSTRUCT thus will likely fail.
> > 
> > How can we know whether a given 'struct tdx_blob' can work on an platform or
> > not?  Or am I missing anything?
> 
> Good question.
> 
> This is actually userspace's responsibility. The kernel exposes P-SEAMLDR
> version to userspace, and for each module, the mapping file [*] lists the
> module's minimum P-SEAMLDR version requirements. This allows userspace to
> determine whether the existing P-SEAMLDR can load a specific TDX blob.
> 
> If the kernel cannot load a module using the current P-SEAMLDR, that's
> userspace's fault.
> 
> *: https://github.com/intel/confidential-computing.tdx.tdx-module.binaries/blob/main/mapping_file.json

Thanks for the info.

In this case, I am not sure why do you need to implement code (patch 13) to
firstly support 4K less SIGSTRUCT (with a confusing doc of 'tdx_blob' layout
definition), but here extend it to 16K in a second patch?

How about just merge this one to patch 13 and point out this fact in
changelog if needed?

E.g.,:

  For a given TDX blob, not all SEAMLDR and TDX module versions support 
  runtime update for it.  Intel publishes the requirement of the minimal
  SEAMLDR and TDX module versions for it.

  There's no hardware/firmware interface that the kernel could use to
  detect and bail out early if such requirement is not met.  It's
  userspace's responsibility to make sure such requirement is met before
	 	
  performing runtime update.

Actually, assuming the new spec which reflects 16KB SIGSTRUCT in
SEAMLDR_PARAMS will be published, I _think_ the fact that "some old SEMALDR
versions only support upto 4K SIGSTRUCT" probably doesn't matter anymore,
especially if we add the above to the changelog.

So I don't quite see why we need to keep this "extend SIGSTRUCT to 16KB" as
a separate patch?

Btw, we also need the updated doc of TDX blob layout too, to reflect what
your code is doing (regarding to how to calculate SIGSTRUCT base/size).

And we need to make sure the TDX blob layout is architectural.