Re: [PATCH v5 17/19] KVM:x86: Enable guest CET supervisor xstate bit support

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

On 8/3/23 06:27, Yang Weijiang wrote:
>   	if (boot_cpu_has(X86_FEATURE_XSAVES)) {
> +		u32 eax, ebx, ecx, edx;
> +
> +		cpuid_count(0xd, 1, &eax, &ebx, &ecx, &edx);
>   		rdmsrl(MSR_IA32_XSS, host_xss);
>   		kvm_caps.supported_xss = host_xss & KVM_SUPPORTED_XSS;
> +		if (ecx & XFEATURE_MASK_CET_KERNEL)
> +			kvm_caps.supported_xss |= XFEATURE_MASK_CET_KERNEL;
>   	}

This is a bit hackish and makes me lean more towards adding support for 
XFEATURE_MASK_CET_KERNEL in host MSR_IA32_XSS (and then possibly hide it 
in the actual calls to XSAVE/XRSTORS for non-guest FPU).

Paolo