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Re: [Xen-devel] Hypercall-page initialization

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] Hypercall-page initialization
From: "Jacob Gorm Hansen" <jacobg@xxxxxxx>
Date: Wed, 24 May 2006 11:55:00 +0200
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On 2/7/06, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:

On 7 Feb 2006, at 18:04, Jacob Gorm Hansen wrote:

>> Or if you want to fill it in from within the domU, how about if we did
>> something like reserve some space of MSRs for Xen use (e.g., hex
>> Bxxxxxxx). Then we could say that, if the guest writes an MFN to a
>> particular one of those MSRs, it gets filled with hypercall-page
>> goodness. :-)
> Hmm would that work in paravirt mode also? I guess Xen would trap the
> exception and do the right thing? I suppose this has the advantage of
> avoiding any hardcoded trap vectors.

Yes, although it does sound kinda gross, it will work and ultimately I
think it sounds quite attractive compared with the alternatives. Not
sure how to decide what MSR range to pick to reserve... Apart from that
it's trivial to implement.


I've bumped my head against this again, and a quick fix would be to
make the dom0 op unprivileged. If you can tell me where in the xen
source you would like op to be moved, I send in a patch for it.


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