linux-kernel - Re: [PATCH RFC v7 37/64] KVM: SVM: Add KVM_SNP

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Date:   Mon, 23 Jan 2023 16:49:14 -0600
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Michael Roth <michael.roth@....com>
Cc:     kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
        linux-mm@...ck.org, linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        luto@...nel.org, dave.hansen@...ux.intel.com, slp@...hat.com,
        pgonda@...gle.com, peterz@...radead.org,
        srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
        dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
        vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
        dgilbert@...hat.com, harald@...fian.com,
        Brijesh Singh <brijesh.singh@....com>,
        Pavan Kumar Paluri <papaluri@....com>
Subject: Re: [PATCH RFC v7 37/64] KVM: SVM: Add KVM_SNP_INIT command

There was an early firmware issue on Genoa which supported only SNP_INIT 
or SEV_INIT, but this issue is resolved now.

Now, the main constraints are that SNP_INIT is always required before 
SEV_INIT in case we want to launch SNP guests. In other words, if only 
SEV_INIT is done on a platform which supports SNP we won't be able to 
launch SNP guests after that.

So once we have RMP table setup (in BIOS) we will always do an SNP_INIT 
and SEV_INIT will be ideally done only (on demand) when an SEV guest is 
launched.

Thanks,
Ashish

On 1/5/2023 5:37 PM, Kalra, Ashish wrote:
> 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