Re: [PATCH v2 00/21] Runtime TDX Module update support

[<dan.j.williams@intel.com>]

Vishal Annapurve wrote:
> On Mon, Oct 27, 2025 at 11:53 AM <dan.j.williams@intel.com> wrote:
> >
> > Vishal Annapurve wrote:
> > [..]
> > > > A theoretical TDX Module change could ensure that atomicity.
> > >
> > > IIUC TDX module already supports avoiding this clobber based on the
> > > TDH.SYS.SHUTDOWN documentation from section 5.4.73 of TDX ABI Spec
> > > [1].
> > >
> > > Host kernel needs to set bit 16 of rcx when invoking TDH.SYS.SHUTDOWN
> > > is available.
> > >
> > > "If supported by the TDX Module, the host VMM can set the
> > > AVOID_COMPAT_SENSITIVE flag to request the TDX Module to fail
> > > TDH.SYS.UPDATE if any of the TDs are currently in a state that is
> > > impacted by the update-sensitive cases."
> >
> > That is not a fix. That just shifts the complexity from build to update.
> > It still leaves update in a state where it is not guaranteed to make
> 
> IMO, there are two problems here:
> 1) Giving a consistent ABI that leaves the responsibility of ensuring
> forward progress by sequencing TD update with TD build steps with
> userspace.
> 2) Ensuring that userspace can't screw up the in-progress TD VM
> metadata if userspace doesn't adhere to the sequence above.
> 
> Problem 2 should be solved in the TDX module as it is the state owner
> and should be given a chance to ensure that nothing else can affect
> it's state. Kernel is just opting-in to toggle the already provided
> TDX module ABI. I don't think this is adding complexity to the kernel.

That gives update a transient error to handle