Re: Drop "KVM: TDX: Handle TDG.VP.VMCALL<GetTdVmCallInfo> hypercall"

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

+Kirill

Context:
https://lore.kernel.org/kvm/da3e2f6bdc67b1b02d99a6b57ffc9df48a0f4743.camel@intel.com/

On Fri, 2025-04-18 at 15:24 +0200, Paolo Bonzini wrote:
> It does, but I think we should just implement the remaining TDVMCALLs 
> before 6.16 is out, which is in a while.  All that is left is really the 
> userspace TDVMCALLs GetQuote, ReportFatalError and 
> SetupEventNotifyInterrupt.
> 
> For Instruction.PCONFIG and for VE.RequestMMIO a dummy implementation is 
> valid and returning success is probably even better than invalid-operand.

You might be looking at the 1.0 spec. The 1.5 spec has the same GetTdVmCallInfo
success criteria of supporting all calls, but adds a couple more. Here are the
missing calls listed in the 1.5 spec.

TDG.VP.VMCALL<GETQUOTE> - Have patches, but missing
TDG.VP.VMCALL<SETUPEVENTNOTIFYINTERRUPT> - Have patches, but missing
TDG.VP.VMCALL<INSTRUCTION.WBINVD> - Missing
TDG.VP.VMCALL<INSTRUCTION.PCONFIG> - Missing
TDG.VP.VMCALL<Service.Query> - Missing
TDG.VP.VMCALL<Service.MigTD> - Missing

The GHCI also has the following disclaimer:
"This document is a work in progress and is subject to change based on customer
feedback and internal analysis."

So I'm not sure if following the GetTdVmCallInfo spec to the letter is worth the
cost of too much dead code, compared to asking them to update it. How were you
looking at it? In any case we can prep some minimal implementations and see how
it looks.

Xiaoyao was tossing around the idea of adding a dedicated "not implemented"
return code too. It could make it simpler to evolve the GHCI spec vs the all or
nothing approach. To me, the main finding here is that we need to have more
clarity on how the GHCI will evolve going forward.