linux-kernel - Re: [PATCH Part2 v5 23/45] KVM: SVM: Add KVM_SNP

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Date:   Tue, 14 Jun 2022 09:37:39 -0600
From:   Peter Gonda <pgonda@...gle.com>
To:     Ashish Kalra <ashkalra@....com>
Cc:     Alper Gun <alpergun@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ashish Kalra <Ashish.Kalra@....com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>, linux-coco@...ts.linux.dev,
        linux-mm@...ck.org,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>, Marc Orr <marcorr@...gle.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Pavan Kumar Paluri <papaluri@....com>
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@....com> wrote:
>
>
> On 6/13/22 23:33, Alper Gun wrote:
> > On Mon, Jun 13, 2022 at 4:15 PM Ashish Kalra <ashkalra@....com> 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().

>
> Thanks, Ashish
>