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Date: Tue, 29 Jan 2013 16:14:39 +0000
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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To: KY Srinivasan <kys@microsoft.com>
CC: Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>,
        Olaf Hering <olaf@aepfle.de>, Jan Beulich <JBeulich@suse.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] x86: Hyper-V: register clocksource only if its
 advertised
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On Tue, 29 Jan 2013, KY Srinivasan wrote:
> > > I agree with you that your patch is valid for making the Hyper-V code more
> > robust but not for dealing
> > > with general issue of Xen emulating Hyper-V.
> > 
> > What "general issue" would that be?
> 
> Not all Hyper-V specific features are advertised via a feature bit. For instance, we need to reserve
> an IDT entry to have VMBUS interrupts delivered on a per-CPU basis and this reservation is done
> after confirming that we are running on Hyper-V. With Xen emulating Hyper-V, we have an issue.
> Since Hyper-V will never emulate Xen, I am going to add a check in the Hyper-V detection code to
> deal with this issue.

I personally think that it would be much nicer to have a feature flag
somewhere to advertise per-CPU VMBUS interrupts.
However adding a check in the Hyper-V detection code is OK too for me.