Re: [PATCH v15 11/41] KVM: x86: Report KVM supported CET MSRs as to-be-saved

[Binbin Wu]

On 9/13/2025 7:22 AM, Sean Christopherson wrote:
> From: Yang Weijiang <weijiang.yang@xxxxxxxxx>
>
> Add CET MSRs to the list of MSRs reported to userspace if the feature,
> i.e. IBT or SHSTK, associated with the MSRs is supported by KVM.
>
> Suggested-by: Chao Gao <chao.gao@xxxxxxxxx>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> Tested-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
> Tested-by: John Allen <john.allen@xxxxxxx>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>

> ---
>   arch/x86/kvm/x86.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5653ddfe124e..2c9908bc8b32 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -344,6 +344,10 @@ static const u32 msrs_to_save_base[] = {
>   	MSR_IA32_UMWAIT_CONTROL,
>   
>   	MSR_IA32_XFD, MSR_IA32_XFD_ERR, MSR_IA32_XSS,
> +
> +	MSR_IA32_U_CET, MSR_IA32_S_CET,
> +	MSR_IA32_PL0_SSP, MSR_IA32_PL1_SSP, MSR_IA32_PL2_SSP,
> +	MSR_IA32_PL3_SSP, MSR_IA32_INT_SSP_TAB,
>   };
>   
>   static const u32 msrs_to_save_pmu[] = {
> @@ -7598,6 +7602,20 @@ static void kvm_probe_msr_to_save(u32 msr_index)
>   		if (!kvm_caps.supported_xss)
>   			return;
>   		break;
> +	case MSR_IA32_U_CET:
> +	case MSR_IA32_S_CET:
> +		if (!kvm_cpu_cap_has(X86_FEATURE_SHSTK) &&
> +		    !kvm_cpu_cap_has(X86_FEATURE_IBT))
> +			return;
> +		break;
> +	case MSR_IA32_INT_SSP_TAB:
> +		if (!kvm_cpu_cap_has(X86_FEATURE_LM))
> +			return;
> +		fallthrough;
> +	case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
> +		if (!kvm_cpu_cap_has(X86_FEATURE_SHSTK))
> +			return;
> +		break;
>   	default:
>   		break;
>   	}