Re: [PATCH v2 0/3] TDX attestation support and GHCI fixup

["Edgecombe, Rick P" <rick.p.edgecombe@intel.com>]

On Fri, 2025-06-20 at 19:24 +0200, Paolo Bonzini wrote:
> On Fri, Jun 20, 2025 at 2:48 PM Xiaoyao Li <xiaoyao.li@intel.com> wrote:
> > > The interface I chose is that KVM always exits, but it initializes the
> > > output values such that userspace can leave them untouched for unknown
> > > TDVMCALLs or unknown leaves. So there is no need for this.
> > > 
> > > Querying kernel support of other services can be added later, but
> > > unless the GHCI adds more input or output fields to TdVmCallInfo there
> > > is no need to limit the userspace exit to leaf 1.
> > 
> > I meant the case where KVM is going to support another optional TDVMCALL
> > leaf in the future, e.g., SetEventNotifyInterrupt. At that time,
> > userspace needs to differentiate between old KVM which only supports
> > <GetQuote> and new KVM which supports both <GetQuote> and
> > <SetEventNotifyInterrupt>.
> 
> Yeah, I see what you mean now. Userspace cannot know which TDVMCALL
> will exit, other than GET_QUOTE which we know is in the first part.

How about we expose the KVM supported GHCI exits in KVM_TDX_CAPABILITIES? We had
been discussing this as an option. It is not needed for the initial fixup series
I think.

It can include GHCI calls handled within KVM, and ones that are supported via
exits.

> 
> By the way I'm tempted to implement SetupEventNotifyInterrupt as well,
> it's just a handful of lines of code.

Seems ok to me. In general I think we should lean towards implementing the
minimum. It seems we are still in the learning period and have already had some
TDX arch course corrections. If a GetQuote2, SetEventNotifyInterrupt2, etc shows
up, it all starts to add up. Having a KVM_EXIT_TDX will help there, from the KVM
side at least.