RE: [Xen-devel] [PATCH] [VTD] Separate VT-d page table from P2M table

["Han, Weidong" <weidong.han@xxxxxxxxx>]

Ian Pratt wrote:
>> If EPT supports 2MB page, we need separate VT-d table to let them
>> work together.
> 
> Are you saying that the VT-d 2MB page format is different from the EPT
> 2MB page format? Or that VTd does not support 2MB pages?
> 

Now VTd does not support 2MB pages.

> Ian
> 
>> What's more, sharing makes coupling between VT-d page table
>> and p2m table. In case VT-d spec changes or p2m structure changes,
>> shared table will be broken.
> 
>> Randy (Weidong)
>> 
>> Keir Fraser wrote:
>>> What are the tradeoffs? One obvious tradeoff is that separate tables
>>> doubles the memory overhead. What are the advantages of separate
>>> tables? I believe currently we share the pagetables (right?). If so,
>>> why would we even consider moving to separate tables?
>>> 
>>>  -- Keir
>>> 
>>> On 22/4/08 10:34, "Han, Weidong" <weidong.han@xxxxxxxxx> wrote:
>>> 
>>>> Separate VT-d page table is by default. Shared VT-d page table may
>>>> be easy and good in some cases. So we let them co-exist now. If
>>>> shared VT-d page table is not necessary and useless, we can remove
>>>> it easily in future. 
>>>> 
>>>> Randy (weidong)
>>>> 
>>>> Keir Fraser wrote:
>>>>> On 22/4/08 09:36, "Han, Weidong" <weidong.han@xxxxxxxxx> wrote:
>>>>> 
>>>>>> Currently VT-d page table shares with P2M table, this patch
>>>>>> supports separate VT-d page table. 1) add an option (vtd_share)
>>>>>> to control whether VT-d page table shares with P2M table or not.
>>>>> 
>>>>> Why? Is this just another option that noone will understand.
>>>>> 
>>>>>  -- Keir
>> 
>> 
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