Re: [PATCH] KVM: MMU: update comment on the number of page role combinations

[Paolo Bonzini]

On 11/17/21 23:25, Sean Christopherson wrote:
> > Here is a better writeup:
> >
> >   *   - invalid shadow pages are not accounted, so the bits are effectively 18
> >   *   - quadrant will only be used if gpte_is_8_bytes is zero (non-PAE paging);
> >   *     execonly and ad_disabled are only used for nested EPT which has
> >   *     gpte_is_8_bytes=1.  Therefore, 2 bits are always unused.
> >   *   - the 4 bits of level are effectively limited to the values 2/3/4/5,
> >   *     as 4k SPs are not tracked (allowed to go unsync).  In addition non-PAE
> >   *     paging has exactly one upper level, making level effectively redundant
> >   *     when gpte_is_8_bytes=0.
> >   *   - on top of this, smep_andnot_wp and smap_andnot_wp are only set if cr0_wp=0,
> >   *     therefore these three bits only give rise to 5 possibilities.
> >
> > FWIW, the full count becomes 6400 unless I screwed up the math.
> Which is "in the neighborhood of 2^13":-)

2^12 if SMM is not counted.

Paolo