Re: [PATCH v8 44/55] i386/tdx: Implement adjust_cpuid_features() for TDX

[Zhao Liu <zhao1.liu@intel.com>]

On Tue, Apr 01, 2025 at 09:01:54AM -0400, Xiaoyao Li wrote:
> Date: Tue,  1 Apr 2025 09:01:54 -0400
> From: Xiaoyao Li <xiaoyao.li@intel.com>
> Subject: [PATCH v8 44/55] i386/tdx: Implement adjust_cpuid_features() for
>  TDX
> X-Mailer: git-send-email 2.34.1
> 
> Maintain a TDX specific supported CPUID set, and use it to mask the
> common supported CPUID value of KVM. It can avoid newly added supported
> features (reported via KVM_GET_SUPPORTED_CPUID) for common VMs being
> falsely reported as supported for TDX.
> 
> As the first step, initialize the TDX supported CPUID set with all the
> configurable CPUID bits. It's not complete because there are other CPUID
> bits are supported for TDX but not reported as directly configurable.
> E.g. the XFAM related bits, attribute related bits and fixed-1 bits.
> They will be handled in the future.
> 
> Also, what matters are the CPUID bits related to QEMU's feature word.
> Only mask the CPUID leafs which are feature word leaf.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
>  target/i386/cpu.c          | 18 ++++++++++++++++++
>  target/i386/cpu.h          |  1 +
>  target/i386/kvm/kvm.c      |  2 +-
>  target/i386/kvm/kvm_i386.h |  1 +
>  target/i386/kvm/tdx.c      | 34 ++++++++++++++++++++++++++++++++++
>  5 files changed, 55 insertions(+), 1 deletion(-)

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>

> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index f219961b62cd..4061d38d3fbe 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -1655,6 +1655,24 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>      },
>  };
>  
> +bool is_feature_word_cpuid(uint32_t feature, uint32_t index, int reg)
> +{
> +    FeatureWordInfo *wi;
> +    FeatureWord w;
> +
> +    for (w = 0; w < FEATURE_WORDS; w++)
> +    {

(style nit?) "{" should be at the end of the previous line?

> +        wi = &feature_word_info[w];
> +        if (wi->type == CPUID_FEATURE_WORD && wi->cpuid.eax == feature &&
> +            (!wi->cpuid.needs_ecx || wi->cpuid.ecx == index) &&
> +            wi->cpuid.reg == reg)
> +        {

ditto.

> +            return true;
> +        }
> +    }
> +    return false;
> +}
> +