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

To: "Li, Xin B" <xin.b.li@xxxxxxxxx>, "Han, Weidong" <weidong.han@xxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] [VTD] Separate VT-d page table from P2M table
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 22 Apr 2008 18:44:53 +0100
Cc: "Xu, Anthony" <anthony.xu@xxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>
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On 22/4/08 16:43, "Li, Xin B" <xin.b.li@xxxxxxxxx> wrote:

>> Then don't allow EPT 2MB mappings for domains which have
>> passthru devices?
> EPT 2M page is already supported while VT-d 2M not, so for we have to
> seperate the 2 guys if we want to use 2M page in EPT.
> and of course we share the page tables if both sides use 4K pages.

Just share the tables and put up with not having 2MB mappings available to
you if a guest has devices passed through to it? Doesn't sound so bad to me,
and you can get the performance back down the line by fixing the VT-d
hardware to understand superpage mappings. We're going to end up with a
silly number of p2m structures otherwise.

 -- Keir

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