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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

> > 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

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