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

Ashish Kalra
2022-06-14T00:21:31Z

On 6/13/22 23:33, Alper Gun wrote:
> On Mon, Jun 13, 2022 at 4:15 PM Ashish Kalra <ashkalra@amd.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