linux-kernel - RE: [PATCH] x86: Hyper-V: register clocksource only if its advertised

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Message-ID: <alpine.DEB.2.02.1301291611270.10432@kaball.uk.xensource.com>
Date:	Tue, 29 Jan 2013 16:14:39 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	KY Srinivasan <kys@...rosoft.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	Olaf Hering <olaf@...fle.de>, Jan Beulich <JBeulich@...e.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] x86: Hyper-V: register clocksource only if its
 advertised

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.
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