Re: [PATCH RFC v7 37/64] KVM: SVM: Add KVM_SNP_INIT command

[Kalra, Ashish]

Hello Jarkko,

On 12/31/2022 8:27 AM, Jarkko Sakkinen wrote:
> On Wed, Dec 14, 2022 at 01:40:29PM -0600, Michael Roth wrote:
> >   static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
> >   {
> >   	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > @@ -260,13 +279,23 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
> >   		return ret;
> >   
> >   	sev->active = true;
> > -	sev->es_active = argp->id == KVM_SEV_ES_INIT;
> > +	sev->es_active = (argp->id == KVM_SEV_ES_INIT || argp->id == KVM_SEV_SNP_INIT);
> > +	sev->snp_active = argp->id == KVM_SEV_SNP_INIT;
> >   	asid = sev_asid_new(sev);
> >   	if (asid < 0)
> >   		goto e_no_asid;
> >   	sev->asid = asid;
> >   
> > -	ret = sev_platform_init(&argp->error);
> > +	if (sev->snp_active) {
> > +		ret = verify_snp_init_flags(kvm, argp);
> > +		if (ret)
> > +			goto e_free;
> > +
> > +		ret = sev_snp_init(&argp->error, false);
> > +	} else {
> > +		ret = sev_platform_init(&argp->error);
> > +	}
>
> Couldn't sev_snp_init() and sev_platform_init() be called unconditionally
> in order?
>
> Since there is a hardware constraint that SNP init needs to always happen
> before platform init, shouldn't SNP init happen as part of
> __sev_platform_init_locked() instead?

On Genoa there is currently an issue that if we do an SNP_INIT before an 
SEV_INIT and then attempt to launch a SEV guest that may fail, so we 
need to keep SNP INIT and SEV INIT separate.

We need to provide a way to run (existing) SEV guests on a system that 
supports SNP without doing an SNP_INIT at all.

This is done using psp_init_on_probe parameter of the CCP module to 
avoid doing either SNP/SEV firmware initialization during module load 
and then defer the firmware initialization till someone launches a guest 
of one flavor or the other.

And then sev_guest_init() does either SNP or SEV firmware init depending 
on the type of the guest being launched.

> I found these call sites for __sev_platform_init_locked(), none of which
> follow the correct call order:
>
> * sev_guest_init()

As explained above, this call site is important for deferring the 
firmware initialization to an actual guest launch.

> * sev_ioctl_do_pek_csr
> * sev_ioctl_do_pdh_export()
> * sev_ioctl_do_pek_import()
> * sev_ioctl_do_pek_pdh_gen()
> * sev_pci_init()
>
> For me it looks like a bit flakky API use to have sev_snp_init() as an API
> call.
>
> I would suggest to make SNP init internal to the ccp driver and take care
> of the correct orchestration over there.

Due to Genoa issue, we may still need SNP init and SEV init to be 
invoked separately outside the CCP driver.

> Also, how it currently works in this patch set, if the firmware did not
> load correctly, SNP init halts the whole system. The version check needs
> to be in all call paths.

Yes, i agree with that.

Thanks,
Ashish