Re: [PATCH v3 2/5] KVM: MMU: check guest CR3 reserved bits based on its physical address width.

Paolo Bonzini
2017-08-24T15:50:17Z

On 24/08/2017 17:23, Yu Zhang wrote:
>>>
>>> static inline u64 rsvd_bits(int s, int e)
>>> {
>>> + if (e < s)
>>> + return 0;
>>> +
>>> return ((1ULL << (e - s + 1)) - 1) << s;
>>> }
>> e = s - 1 is already supported; why do you need e <= s - 2?
>
> Sorry? I do not quite understand. When will e = s - 1?

Is there any case where e < s? I can see that MAXPHYADDR=63 gives
rsvd_bits(63, 62), but that works.

In practice, MAXPHYADDR will never be 59 even because the PKRU bits are
at bits 59..62.

Paolo