Re: [PATCH v4 1/4] KVM: TDX: Track configurable CPUID bits allowed by KVM

[Edgecombe, Rick P]

On Wed, 2026-09-23 at 08:14 +0800, Binbin Wu wrote:
> > Sorry, I'm not following this logic exactly. The guest can control it's own
> > view
> > of CPUID. Why do we need to filter the host setting them via direct
> > configuration, just because the guest can change it's view to exclude them?
> 
> 
> These feature neither supported by the TDX module nor supported by the KVM.
> If the guest enabled the #VE reduction, the access to the related MSRs will
> cause #GP. If the guest doesn't enabled the #VE redcution, #VE cannot be
> supported by KVM since the related MSRs are not support by KVM.
> 
> So the guest cannot use these features anyway.

But directly configurable bits don't have any direct conntion to tdcall queried
bits. Userspace can still set those to whatever it wants regardless of the allow
list. 

So the argument is basically there is not expected to be any reason to allow
them, so save the code in the allow list. It's a "there is no point" reason.
Makes sense, but I couldn't get that from explanation.