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

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Message-ID: <20130125171923.GA19306@aepfle.de>
Date:	Fri, 25 Jan 2013 18:19:23 +0100
From:	Olaf Hering <olaf@...fle.de>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"Jan Beulich (JBeulich@...e.com)" <JBeulich@...e.com>
Subject: Re: [PATCH] x86: Hyper-V: register clocksource only if its advertised

On Fri, Jan 25, KY Srinivasan wrote:

> My fear is that there is no guarantee that Xen would not emulate this
> feature in the spirit of making Hyper-V emulation "more" complete.
> Since all this problem is because Xen thinks it is running a viridian
> domain (when in fact it is running Linux), I felt we should explore
> why the viridian tag got set for a Linux VM. If we can fix that we
> would have a solution that does not depend upon assuming that Xen
> would not emulate a particular Hyper-V feature.

In my opinion this logic is backwards. A host provides a set of
functionality/features to a given guest, no matter what runs inside the
guest. And the guest can query the feature list and configure itself
accordingly. In this specific case the guest finds feature A (the cpuid
result) and expects that feature B (a clock source) is present as well,
even if feature B has its very own availability flag.

Maybe I miss your point.

Olaf
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