linux-kernel - Re: [PATCH 05/16] KVM-HDR: Implement wallclock over KVM

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Date:	Wed, 26 Jan 2011 10:20:03 -0200
From:	Glauber Costa <glommer@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	aliguori@...ibm.com
Subject: Re: [PATCH 05/16] KVM-HDR: Implement wallclock over KVM - KVM
 Virtual Memory

On Wed, 2011-01-26 at 13:13 +0200, Avi Kivity wrote:
> On 01/24/2011 08:06 PM, Glauber Costa wrote:
> > As a proof of concept to KVM - Kernel Virtual Memory, this patch
> > implements wallclock grabbing on top of it. At first, it may seem
> > as a waste of work to just redo it, since it is working well. But over the
> > time, other MSRs were added - think ASYNC_PF - and more will probably come.
> > After this patch, we won't need to ever add another virtual MSR to KVM.
> >
> 
> So instead of adding MSRs, we're adding area identifiers.  What did we gain?

* No risk of namespace clashes of any kind,
* less need for userspace coordination for feature enablement,
* more robust mechanism that can do discovery even on early boot,
* more informative result values can be passed on to guest kernel, 
* more flexibility, since we go back to userspace if we can't handle
some request. Also, some requests are better handled by userspace
anyway. But again, maybe this is a separate issue here...
* size information goes together with base, allowing for extending
structures (well, maybe I should add versioning explicitly?)

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