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

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