Re: [PATCH Part2 v5 23/45] KVM: SVM: Add KVM_SNP_INIT command

[Ashish Kalra]

On 6/13/22 23:33, Alper Gun wrote:
> On Mon, Jun 13, 2022 at 4:15 PM Ashish Kalra <ashkalra@xxxxxxx> wrote:
> > Hello Alper,
> >
> > On 6/13/22 20:58, Alper Gun wrote:
> > > static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
> > > >    {
> > > > +       bool es_active = (argp->id == KVM_SEV_ES_INIT || argp->id == KVM_SEV_SNP_INIT);
> > > >           struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > > > -       bool es_active = argp->id == KVM_SEV_ES_INIT;
> > > > +       bool snp_active = argp->id == KVM_SEV_SNP_INIT;
> > > >           int asid, ret;
> > > >
> > > >           if (kvm->created_vcpus)
> > > > @@ -249,12 +269,22 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
> > > >                   return ret;
> > > >
> > > >           sev->es_active = es_active;
> > > > +       sev->snp_active = snp_active;
> > > >           asid = sev_asid_new(sev);
> > > >           if (asid < 0)
> > > >                   goto e_no_asid;
> > > >           sev->asid = asid;
> > > >
> > > > -       ret = sev_platform_init(&argp->error);
> > > > +       if (snp_active) {
> > > > +               ret = verify_snp_init_flags(kvm, argp);
> > > > +               if (ret)
> > > > +                       goto e_free;
> > > > +
> > > > +               ret = sev_snp_init(&argp->error);
> > > > +       } else {
> > > > +               ret = sev_platform_init(&argp->error);
> > > After SEV INIT_EX support patches, SEV may be initialized in the platform late.
> > > In my tests, if SEV has not been initialized in the platform yet, SNP
> > > VMs fail with SEV_DF_FLUSH required error. I tried calling
> > > SEV_DF_FLUSH right after the SNP platform init but this time it failed
> > > later on the SNP launch update command with SEV_RET_INVALID_PARAM
> > > error. Looks like there is another dependency on SEV platform
> > > initialization.
> > >
> > > Calling sev_platform_init for SNP VMs fixes the problem in our tests.
> > Trying to get some more context for this issue.
> >
> > When you say after SEV_INIT_EX support patches, SEV may be initialized
> > in the platform late, do you mean sev_pci_init()->sev_snp_init() ...
> > sev_platform_init() code path has still not executed on the host BSP ?
> Correct, INIT_EX requires the file system to be ready and there is a
> ccp module param to call it only when needed.
>
> MODULE_PARM_DESC(psp_init_on_probe, " if true, the PSP will be
> initialized on module init. Else the PSP will be initialized on the
> first command requiring it");
>
> If this module param is false, it won't initialize SEV on the platform
> until the first SEV VM.
Ok, that makes sense.

So the fix will be to call sev_platform_init() unconditionally here in 
sev_guest_init(), and both sev_snp_init() and sev_platform_init() are 
protected from being called again, so there won't be any issues if these 
functions are invoked again at SNP/SEV VM launch if they have been 
invoked earlier during module init.

Thanks, Ashish