> On Mon, 2024-03-25 at 11:14 +0000, Huang, Kai wrote: > > To confirm, I mean you want to simply make KVM_SET_CPUID2 return error > > for TDX guest? > > > > It is acceptable to me, and I don't see any conflict with Sean's comments. > > > > But I don't know Sean's perference. As he said, I think the > > consistency checking is quite straight-forward: > > > > " > > It's not complicated at all. Walk through the leafs defined during > > TDH.MNG.INIT, reject KVM_SET_CPUID if a leaf isn't present or doesn't > > match exactly. > > " > > > Yea, I'm just thinking if we could take two patches down to one small one it > might be a way to essentially break off this work to another series without > affecting the ability to boot a TD. It > *seems* to be the way things are going. > > > So to me it's not a big deal. > > > > Either way, we need a patch to handle SET_CPUID2: > > > > 1) if we go option 1) -- that is reject SET_CPUID2 completely -- we > > need to make vcpu's CPUID point to KVM's saved CPUID during > TDH.MNG.INIT. > > Ah, I missed this part. Can you elaborate? By dropping these two patches it > doesn't prevent a TD boot. If we then reject SET_CPUID, this will break things > unless we make other changes? And they are not small? > (sorry replying from outlook due to some issue to my linux box environment) It booted because Qemu does sane thing, i.e., it always passes the correct CPUIDs in KVM_SET_CPUID2. Per-Sean's comments, KVM should guarantee the consistency between CPUIDs done in TDH.MNG.INIT and KVM_SET_CPUID2, otherwise if Qemu passes in-consistent CPUIDs KVM can easily fail to work with TD. To guarantee the consistency, KVM could do two options as we discussed: 1) reject KVM_SET_CPUID2 completely. 2) Still allow KVM_SET_CPUID2 but manually check the CPUID consistency between the one done in TDH.MNG.INIT and the one passed in KVM_SET_CPUID2. 1) can obviously guarantee consistency. But KVM maintains CPUIDs in 'vcpu', so to make the existing KVM code continue to work, we need to manually set 'vcpu->cpuid' to the one that is done in TDH.MNG.INIT. 2) you need to check the consistency and reject KVM_SET_CPUID2 if in-consistency found. But other than that, KVM doesn't need to anything more because if we allow KVM_SET_CPUID2, the 'vcpu' will have its own CPUIDs populated anyway.
