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Re: [Xen-devel] [PATCH 06/16] vmx: nest: handling VMX instruction exits

To: "Dong, Eddie" <eddie.dong@xxxxxxxxx>, Christoph Egger <Christoph.Egger@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 06/16] vmx: nest: handling VMX instruction exits
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 20 Sep 2010 10:41:40 +0100
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, "He, Qing" <qing.he@xxxxxxxxx>
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Thread-topic: [Xen-devel] [PATCH 06/16] vmx: nest: handling VMX instruction exits
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On 20/09/2010 10:33, "Dong, Eddie" <eddie.dong@xxxxxxxxx> wrote:

>> Are you suggesting to always emulate instead of always inject-to-L1?
>> That's still not accurate virtualisation of this VMX feature.
> L2 PIO is always exiting to L0. So we wither inject to L1, or emulate it in
> L0, base on L1 I/O exiting and bitmap setting.
>> Hmm... Are you currently setting up to always vmexit on I/O port
>> accesses by L2? Even if you are, that doesn't stop you looking at the
> Yes.
>> virtual I/O bitmap from in your L0 vmexit handler, and doing the
> No, we checked the L1 settings.

Right, okay, I think this issue about write-protecting the I/O bitmap and
maintaining an accurate shadow bitmap is entirely orthogonal to the issue of
emulation versus injection. The former issue is a performance optimisation
only afaics, and I wouldn't care about that in a first checkin of nestedhvm.

 -- Keir

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