Re: [RFC PATCH v2 0/4] KVM: x86: TDX: Validate directly configurable CPUID bits

[Sean Christopherson <seanjc@google.com>]

On Mon, Jun 22, 2026, Binbin Wu wrote:
> On 6/4/2026 10:33 AM, Binbin Wu wrote:
> > Hi,
> > 
> > A host state clobbering feature on new TDX modules/platforms can lead
> > to host state corruption if KVM does not explicitly save and restore
> > the related MSR(s) during host/guest transitions. If such a feature is
> > blindly exposed to and used by TDs, it will result in unexpected behavior
> > on the host.
> > 
> > The v1 RFC [1] attempted to solve this by introducing a comprehensive
> > CPUID paranoid verification framework across VMX, SVM, and TDX. However,
> > as Sean pointed out in [2] and the discussion in the PUCK meeting, this
> > approach was overly complex and bled too many TDX-specific details into
> > common KVM code, creating an unnecessary maintenance burden.
> > 
> > This v2 takes a significantly simpler, TDX-contained approach. It strictly
> > validates only the TDX directly configurable CPUID bits—those reported by
> > the TDX module in CPUID_CONFIG fields that the VMM can configure for a TD.
> > This is sufficient to address the host clobbering issue, as no new host
> > state clobbering features will be fixed-1. All filtering and validation
> > logic is entirely isolated within TDX code.
> > 
> > Feedback is highly appreciated, particularly on whether this contained
> > approach strikes an acceptable balance regarding complexity.
> 
> Hi Sean,
> 
> Do you think this proposal is the direction to go?

Yeah, the basic gist looks good.