On Fri, 2024-10-18 at 10:21 +0800, Xiaoyao Li wrote: > > KVM usually leaves it up to userspace to not create nonsensical VMs. So I > > think > > we can skip the check in KVM. > > It's not nonsensical unless KVM announces its own requirement for TD > guest that userspace VMM must provide valid CPUID leaf 0x1f value for > topology. How about adding it to the docs? > > It's architectural valid that userspace VMM creates a TD with legacy > topology, i.e., topology enumerated via CPUID 0x1 and 0x4. > > > In that case, do you see a need for the vanilla tdh_vp_init() SEAMCALL > > wrapper? > > > > The TDX module version we need already supports enum_topology, so the code: > > if (modinfo->tdx_features0 & MD_FIELD_ID_FEATURES0_TOPOLOGY_ENUM) > > err = tdh_vp_init_apicid(tdx, vcpu_rcx, vcpu->vcpu_id); > > else > > err = tdh_vp_init(tdx, vcpu_rcx); > > > > The tdh_vp_init() branch shouldn't be hit. > > We cannot know what version of TDX module user might use thus we cannot > assume enum_topology is always there unless we make it a hard > requirement in KVM that TDX fails being enabled when > > !(modinfo->tdx_features0 & MD_FIELD_ID_FEATURES0_TOPOLOGY_ENUM) We will depend on bugs that are fixed in TDX Modules after enum topology, so it shouldn't be required in the normal case. So I think it would be simpler to add this tdx_features0 conditional. We can then export one less SEAMCALL and will have less configurations flows to worry about on the KVM side.
