On Tue, Aug 13, 2024 at 03:24:32PM +0800, Binbin Wu wrote: > > > >On 8/13/2024 11:25 AM, Chao Gao wrote: >> On Mon, Aug 12, 2024 at 03:48:05PM -0700, Rick Edgecombe wrote: >> > From: Xiaoyao Li <xiaoyao.li@xxxxxxxxx> >> > >> > While TDX module reports a set of capabilities/features that it >> > supports, what KVM currently supports might be a subset of them. >> > E.g., DEBUG and PERFMON are supported by TDX module but currently not >> > supported by KVM. >> > >> > Introduce a new struct kvm_tdx_caps to store KVM's capabilities of TDX. >> > supported_attrs and suppported_xfam are validated against fixed0/1 >> > values enumerated by TDX module. Configurable CPUID bits derive from TDX >> > module plus applying KVM's capabilities (KVM_GET_SUPPORTED_CPUID), >> > i.e., mask off the bits that are configurable in the view of TDX module >> > but not supported by KVM yet. >> > >> > KVM_TDX_CPUID_NO_SUBLEAF is the concept from TDX module, switch it to 0 >> > and use KVM_CPUID_FLAG_SIGNIFCANT_INDEX, which are the concept of KVM. >> If we convert KVM_TDX_CPUID_NO_SUBLEAF to 0 when reporting capabilities to >> QEMU, QEMU cannot distinguish a CPUID subleaf 0 from a CPUID w/o subleaf. >> Does it matter to QEMU? > >According to "and use KVM_CPUID_FLAG_SIGNIFCANT_INDEX, which are the >concept of KVM". IIUC, KVM's ABI uses KVM_CPUID_FLAG_SIGNIFCANT_INDEX >in flags of struct kvm_cpuid_entry2 to distinguish whether the index >is significant. If KVM doesn't indicate which CPU leaf doesn't support subleafs when reporting TDX capabilities, how can QEMU know whether it should set the KVM_CPUID_FLAG_SIGNIFICANT_INDEX flag for a given CPUID leaf? Or is the expectation that QEMU can discover that on its own?
