Re: [PATCH v2 19/31] iommu/vt-d: Reserve the MSB domain ID bit for the TDX module

[Xu Yilun <yilun.xu@linux.intel.com>]

> > > btw in patch23 commit msg:
> > >
> > > "
> > > There is no dedicated way to enumerate which IOMMU devices support
> > > trusted operations. The host has to call TDH.IOMMU.SETUP on all IOMMU
> > > devices and tell their trusted capability by the return value.
> > > "
> > >
> > > which implies that ecap_tdxc() alone doesn't really report the capability?
> > 
> > Ah, good catch. Let me explain:
> > 
> > ecap_tdxc does report the capability. This bit is special cause both
> > trusted part & untrusted part access it.
> > 
> > For IOMMU driver (which now handles the untrusted part), it can directly
> > query to this bit and decide what to do.
> > 
> > But for tdx-host driver which handles the trusted part, it shouldn't
> > speculate into the IOMMU for capability enumeration. TDX Module has more
> > concerns about trusted capability, including the related I/O stack
> 
> I guess "more concerns" means that there are more conditions for
> TDX module to look at beyond ecap_tdxc(), so it's not appropriate
> for tdx-host driver to check ecap alone.

Exactly. 

> 
> > capabilities e.g. SPDM/IDE cap...  So in patch23 I actually mean we
> > don't have an enumeration SEAMCALL for trusted capability, I will
> > refactor that message:
> > 
> >     There is no dedicated *SEAMCALL* to enumerate which IOMMU devices
> > support
> >     trusted operations...