Re: [PATCH v3 07/15] KVM: MMU: introduce nulls desc

Xiao Guangrong
2013-11-25T10:25:24Z

On 11/25/2013 06:19 PM, Gleb Natapov wrote:
> On Mon, Nov 25, 2013 at 02:11:31PM +0800, Xiao Guangrong wrote:
>>>
>>> For example, nothing prevents lockless walker to move into some
>>> parent_ptes chain, right?
>>
>> No.
>>
>> The nulls can help us to detect this case, for parent_ptes, the nulls points
>> to "shadow page" but for rmaps, the nulls points to slot.arch.rmap. There
>> is no chance that the �rmap" is used as shadow page when slot-lock is held.
>>
> But meanwhile we will write protect non-last level sptes, no? Better to

It will meet the non-last sptes but does not write-protect them since
we have do is_last_spte() check before cmpxchg.

> create separate slab caches for rmap and parent_ptes lists.

Yes, this is a good idea. Thanks you, Gleb!