Re: [PATCH] KVM: nVMX: initialize PML fields in vmcs02

[David Hildenbrand <david@redhat.com>]

On 04.04.2017 15:19, Ladi Prosek wrote:
> On Tue, Apr 4, 2017 at 3:09 PM, David Hildenbrand <david@redhat.com> wrote:
>>
>>>>> +     if (enable_pml) {
>>>>> +             /*
>>>>> +              * Conceptually we want to copy the PML address and index from
>>>>> +              * vmcs01 here, and then back to vmcs01 on nested vmexit. But,
>>>>> +              * since we always flush the log on each vmexit, this happens
>>>>
>>>> we == KVM running in g2?
>>>>
>>>> If so, other hypervisors might handle this differently.
>>>
>>> No, we as KVM in L0. Hypervisors running in L1 do not see PML at all,
>>> this is L0-only code.
>>
>> Okay, was just confused why we enable PML for our nested guest (L2)
>> although not supported/enabled for guest hypervisors (L1). I would have
>> guessed that it is to be kept disabled completely for nested guests
>> (!SECONDARY_EXEC_ENABLE_PML).
>>
>> But I assume that this a mysterious detail of the MMU code I still have
>> to look into in detail.
> 
> L1 doesn't see PML but L0 uses it for its own bookkeeping. So it's
> enabled in vmcs02 (what the CPU uses) but not in vmcs12 (what L1
> sees).

So this looks just fine to me. But as I said, haven't looked that
detailed into the MMU code yet.

-- 

Thanks,

David