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

[Tim Deegan <tim@xxxxxxx>]

At 10:13 +0100 on 24 Sep (1443089607), Andrew Cooper wrote:
> 
> >> 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.

I assumed the enable bit was what we were talking about -- the actual
A/D bits in EPTEs should always be _set_ to avoid extra faults.  So
that sounds like we're already doing the right thing.

Cheers,

Tim.

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