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

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, 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: "Dong, Eddie" <eddie.dong@xxxxxxxxx>
Date: Mon, 20 Sep 2010 21:10:33 +0800
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Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "He, Qing" <qing.he@xxxxxxxxx>
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Thread-topic: [Xen-devel] [PATCH 06/16] vmx: nest: handling VMX instruction exits
Keir Fraser wrote:
> 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. 

Yes, that is what I mean. I fixed it locally w/ emulation in L0 + "always 
exit", and we may enhance by maintaining an accurate bitmap.

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