On 4/16/25 05:12, Edgecombe, Rick P wrote:
Hi, We should consider dropping/reverting "KVM: TDX: Handle TDG.VP.VMCALL<GetTdVmCallInfo> hypercall" from the base TDX merge. The reason is because Xiaoyao noticed that the GHCI spec[0] implies that KVM should only return success for that TDVMCALL if *all* TDVMCALLs are supported, but KVM does that despite skipping implementing a few. On investigation there are also no users except its selftest[1], and the spec is ambiguous on the right way to handle the case in question. The spec talks about VMMs not supporting all TDVMCALLs, but doesn't say how to enumerate this (i.e. it doesn't says what the GetTdVmCallInfo VMMs should do instead of succeed). It actually doesn't cover how to handle if the guest calls an unsupported TDVMCALL either. Historically, KVM patches have returned TDVMCALL_STATUS_INVALID_OPERAND for any unknown TDVMCALL, as a reasonable interpretation of the ambiguous spec. So the spec needs to get clarified in this whole area.
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.
Paolo
Since there are no real callers let's just drop GetTdVmCallInfo for now. We can add it back when the GHCI folks amend the spec to close the ambiguities. As a bonus we can save some code for the merge. We dropped the patch internally and did some testing. Also, Binbin and I searched the guest code for any rare callers. Everything seems fine to drop it. If we want to leave it in, it's probably not a disaster. We'll just slightly diverge from the spec. It may not be a problem depending on how the ambiguity resolves in future spec updates. Thanks, Rick [0] https://www.intel.com/content/www/us/en/content-details/726790/guest-host-communication-interface-ghci-for-intel-trust-domain-extensions-intel-tdx.html [1] https://lore.kernel.org/kvm/20250414214801.2693294-14-sagis@xxxxxxxxxx/
