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

To: "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] [VTD] Separate VT-d page table from P2M table
From: "Han, Weidong" <weidong.han@xxxxxxxxx>
Date: Tue, 22 Apr 2008 19:49:22 +0800
Cc: "Xu, Anthony" <anthony.xu@xxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>
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Thread-topic: [Xen-devel] [PATCH] [VTD] Separate VT-d page table from P2M table
If EPT supports 2MB page, we need separate VT-d table to let them work
together. 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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