Re: [PATCH v5 4/5] KVM: TDX: Report only KVM-allowed CPUIDs in KVM_TDX_CAPABILITIES

[Edgecombe, Rick P]

On Fri, 2026-10-16 at 17:14 +0800, Binbin Wu wrote:
> Note, the change is user-visible, as some bits that were previously
> reported as configurable no longer are.  The ABI itself is unchanged: KVM
> already filtered unsupported CPUID bits out of KVM_TDX_CAPABILITIES, albeit
> via a denylist, and the set of configurable bits already varies with the
> TDX module and KVM versions.

I'm not sure what this is saying, the change is user visible but there is no ABI
change? Can't be both... so I think there is an ABI change.

> 
> The change isn't expected to break userspace or guests:
>  - Userspace that honors KVM_TDX_CAPABILITIES simply stops setting the
>    dropped bits, and KVM_TDX_INIT_VM still succeeds.
>  - CORE_CAPABILITIES, which older TDX module specs defined as fixed-1, is
>    still allowed.
>  - The dropped features are either obsolete or unsupported by KVM, and in
>    the latter case, a guest relying on them would already have run into
>    problems.