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SubjectRe: [PATCH 05/16] KVM-HDR: Implement wallclock over KVM - KVM Virtual Memory
On 01/26/2011 02:20 PM, Glauber Costa wrote:
> 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,

That's a bug, not a feature.

> * more robust mechanism that can do discovery even on early boot,

cpuid/wrmsr should be robust enough.

> * more informative result values can be passed on to guest kernel,

True.

> * 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...

Yes.

> * size information goes together with base, allowing for extending
> structures (well, maybe I should add versioning explicitly?)
>

We could do that as well with wrmsr, by having the size as the first
field of the structure. Usually the size isn't really interesting,
though, since you need to discover/enable the new features independently.

--
error compiling committee.c: too many arguments to function



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