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

[Sean Christopherson]

On Mon, Mar 09, 2026, Shivansh Dhiman wrote:
> Hey Sean,
> 
> On 07-03-2026 07:28, Sean Christopherson wrote:
> > 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?
> 
> Yes that's right, the FRED MSRs are zeroed on init.

Please use that as the basis for the changelog.  "Ensure that a vCPU starts with
a clean and valid FRED state on capable hardware" is largely meaningless because
vCPU structures are zero-allocated.