Re: [PATCH 1/7] KVM: SVM: Initialize FRED VMCB fields

[Sean Christopherson]

On Thu, Jan 29, 2026, Shivansh Dhiman wrote:
> From: Neeraj Upadhyay <Neeraj.Upadhyay@xxxxxxx>
> 
> The upcoming AMD FRED (Flexible Return and Event Delivery) feature
> introduces several new fields to the VMCB save area. These fields include
> FRED-specific stack pointers (fred_rsp[0-3], fred_ssp[1-3]), stack level
> tracking (fred_stklvls), and configuration (fred_config).
> 
> Ensure that a vCPU starts with a clean and valid FRED state on
> capable hardware. Also update the size of save areas of VMCB.

> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index f4ccb3e66635..5cec971a1f5a 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1110,6 +1110,16 @@ static void init_vmcb(struct kvm_vcpu *vcpu, bool init_event)
>  	save->idtr.base = 0;
>  	save->idtr.limit = 0xffff;
>  
> +	save->fred_rsp0 = 0;
> +	save->fred_rsp1 = 0;
> +	save->fred_rsp2 = 0;
> +	save->fred_rsp3 = 0;
> +	save->fred_stklvls = 0;
> +	save->fred_ssp1 = 0;
> +	save->fred_ssp2 = 0;
> +	save->fred_ssp3 = 0;
> +	save->fred_config = 0;

Is this architecturally correct?  I.e. are all the FRED MSRs zeroed on INIT?