Re: [PATCH v3 3/4] KVM: TDX: Filter configurable CPUID bits

[Tony Lindgren]

On Tue, Sep 01, 2026 at 04:42:20PM +0800, Binbin Wu wrote:
> On 9/1/2026 2:44 PM, Tony Lindgren wrote:
> > On Thu, Aug 27, 2026 at 11:18:36AM +0800, Binbin Wu wrote:
> >> --- a/arch/x86/kvm/vmx/tdx.c
> >> +++ b/arch/x86/kvm/vmx/tdx.c
> > ...
> >> +static u32 tdx_cfg_non_feature_mask(u32 function, u32 index, int reg)
> >>  {
> >> -	if (has_tsx(entry))
> >> -		clear_tsx(entry);
> >> +	/*
> >> +	 * For a leaf/subleaf/register that will never be repurposed to hold
> >> +	 * feature bits, it's safe to return TDX_CPUID_ALL_ALLOWED_MASK, i.e.
> >> +	 * leave the TDX module's CPUID config mask intact.
> >> +	 */
> >> +	switch (function) {
> >> +	case 1:
> >> +		if (reg == CPUID_EAX || reg == CPUID_EBX)
> >> +			return TDX_CPUID_ALL_ALLOWED_MASK;
> >> +		return 0;
> >> +	case 4:
> >> +	case 0x18:
> >> +	case 0x1f:
> >> +		return TDX_CPUID_ALL_ALLOWED_MASK;
> >> +	case 0x24:
> >> +		if (index == 0 && reg == CPUID_EBX)
> >> +			return GENMASK_U32(7, 0);
> >> +		return 0;
> >> +	case 0x80000008:
> >> +		if (reg == CPUID_EAX)
> >> +			return TDX_CPUID_ALL_ALLOWED_MASK;
> >> +		return 0;
> >> +	default:
> >> +		return 0;
> >> +	}
> >> +}
> > 
> > How about rename the above to something simpler like tdx_get_cpuid_bits()?
> > Sorry I don't have anything better to suggest for naming.
> > 
> >> +static u32 tdx_cfg_feature_mask(u32 function, u32 index, int reg)
> >> +{
> >> +	for (int i = 0; i < NR_KVM_CPU_CAPS; i++) {
> >> +		const struct cpuid_reg *cpuid = &reverse_cpuid[i];
> >> +
> >> +		if (!cpuid->function)
> >> +			continue;
> >> +
> >> +		if (cpuid->function == function && cpuid->index == index &&
> >> +		    cpuid->reg == reg)
> >> +			return tdx_cpu_cfg_caps[i];
> >> +	}
> >> +
> >> +	return 0;
> >>  }
> > 
> > And then the above to tdx_get_cpuid_feature_bits()?
> >   
> >> -static bool tdx_unsupported_cpuid(const struct kvm_cpuid_entry2 *entry)
> >> +static u32 tdx_get_allowed_cfg_cpuid_mask(u32 function, u32 index, int reg)
> >>  {
> >> -	return has_tsx(entry) || has_waitpkg(entry);
> >> +	u32 non_feature_mask = tdx_cfg_non_feature_mask(function, index, reg);
> >> +
> >> +	if (non_feature_mask == TDX_CPUID_ALL_ALLOWED_MASK)
> >> +		return TDX_CPUID_ALL_ALLOWED_MASK;
> >> +
> >> +	/*
> >> +	 * It's possible that a CPUID register contains both feature and
> >> +	 * non-feature bits.
> >> +	 */
> >> +	return non_feature_mask | tdx_cfg_feature_mask(function, index, reg);
> >>  }
> > 
> > And then tdx_get_cpuid_mask()?
> 
> How about:
> tdx_get_cpuid_cfg_non_feature_mask()
> tdx_get_cpuid_cfg_feature_mask()
> tdx_get_cpuid_cfg_mask()

I'd be happy with that.