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

[Kalra, Ashish]

[AMD Official Use Only - General]


-----Original Message-----
From: Peter Gonda <pgonda@xxxxxxxxxx> 
Sent: Tuesday, June 14, 2022 10:38 AM
To: Kalra, Ashish <Ashish.Kalra@xxxxxxx>
Cc: Alper Gun <alpergun@xxxxxxxxxx>; Brijesh Singh <brijesh.singh@xxxxxxx>; Kalra, Ashish <Ashish.Kalra@xxxxxxx>; the arch/x86 maintainers <x86@xxxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>; kvm list <kvm@xxxxxxxxxxxxxxx>; linux-coco@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; Linux Crypto Mailing List <linux-crypto@xxxxxxxxxxxxxxx>; Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Ingo Molnar <mingo@xxxxxxxxxx>; Joerg Roedel <jroedel@xxxxxxx>; Lendacky, Thomas <Thomas.Lendacky@xxxxxxx>; H. Peter Anvin <hpa@xxxxxxxxx>; Ard Biesheuvel <ardb@xxxxxxxxxx>; Paolo Bonzini <pbonzini@xxxxxxxxxx>; Sean Christopherson <seanjc@xxxxxxxxxx>; Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>; Wanpeng Li <wanpengli@xxxxxxxxxxx>; Jim Mattson <jmattson@xxxxxxxxxx>; Andy Lutomirski <luto@xxxxxxxxxx>; Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>; Sergio Lopez <slp@xxxxxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>; David Rientjes <rientjes@xxxxxxxxxx>; Dov Murik <dovmurik@xxxxxxxxxxxxx>; Tobin Feldman-Fitzthum <tobin@xxxxxxx>; Borislav Petkov <bp@xxxxxxxxx>; Roth, Michael <Michael.Roth@xxxxxxx>; Vlastimil Babka <vbabka@xxxxxxx>; Kirill A . Shutemov <kirill@xxxxxxxxxxxxx>; Andi Kleen <ak@xxxxxxxxxxxxxxx>; Tony Luck <tony.luck@xxxxxxxxx>; Marc Orr <marcorr@xxxxxxxxxx>; Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>; Pavan Kumar Paluri <papaluri@xxxxxxx>
Subject: Re: [PATCH Part2 v5 23/45] KVM: SVM: Add KVM_SNP_INIT command

On Mon, Jun 13, 2022 at 6:21 PM Ashish Kalra <ashkalra@xxxxxxx> wrote:
>
>
> 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.

>That's one solution. I don't know if there is a downside to the system for enabling SEV if SNP is being enabled but another solution could be to just directly place a DF_FLUSH command instead of calling sev_platform_init().

Actually sev_platform_init() is already called on module init if psp_init_on_probe is not false. Only need to ensure that SNP firmware is initialized first with SNP_INIT command.

Thanks,
Ashish