Re: [PATCH for-4.6] p2m/ept: Set the A bit only if PML is enabled

[Andrew Cooper <andrew.cooper3@citrix.com>]

>> etc along with adjusting the existing gating of PML on AD being
>> available (perhaps by simply stripping the respective bit from what
>> we read from MSR_IA32_VMX_EPT_VPID_CAP). Of course this
>> then ignores the fact that the erratum only affects the A bit, but
>> I think we can live with that.
>>
>> I also think the currently slightly strange setting of the ept_ad bit
>> should be changed: There's no point setting the bit for domains
>> not getting PML enabled (and incurring the overhead of the
>> hardware updating the bits); imo this should instead be done in
>> ept_enable_pml() / vmx_domain_enable_pml() (and undone in
>> the respective disable function).
> Yep.

Just as a note, in the non PML case, the AD enable bit in EPTP is left 
clear, which means that the A/D bits in the EPTs have no effect.

Therefore, despite the unconditional setting of the A/D bits, there is 
still no MMU overhead.

~Andrew