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

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Message-ID: <ee1a829f-9a89-e447-d182-877d4033c96a@amd.com>
Date:   Tue, 14 Jun 2022 00:21:16 +0000
From:   Ashish Kalra <ashkalra@....com>
To:     Alper Gun <alpergun@...gle.com>
Cc:     Brijesh Singh <brijesh.singh@....com>, Ashish.Kalra@....com,
        x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        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 Gonda <pgonda@...gle.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@...el.com,
        Marc Orr <marcorr@...gle.com>,
        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 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.

Thanks, Ashish