Re: [PATCH 6/6] KVM: VMX: Add PML support in VMX

[Paolo Bonzini <pbonzini@redhat.com>]

On 05/02/2015 07:23, Kai Huang wrote:
>>>
>>> +    /* PML is enabled/disabled in creating/destorying vcpu */
>>> +    exec_control &= ~SECONDARY_EXEC_ENABLE_PML;
>> What is the harm of enabling it here?
>>
>> (SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES seems similar and does it.)
>
> Because the PML feature detection is unconditional (meaning
> SECONDARY_EXEC_ENABLE_PML is always in
> vmcs_config.cpu_based_2nd_exec_ctrl), but the PML buffer is only created
> when vcpu is created, and it is controlled by 'enable_pml' module
> parameter, if we always enable SECONDARY_EXEC_ENABLE_PML here, no PML
> buffer will be created if PML is disabled by 'enable_pml' parameter, so
> it's better to enable it along with creating PML buffer.

I guess this is the most interesting comment from Radim.

Paolo