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SubjectRe: [PATCH 05/16] KVM-HDR: Implement wallclock over KVM - KVM Virtual Memory
On 01/26/2011 05:45 PM, Glauber Costa wrote:
> On Wed, 2011-01-26 at 17:17 +0200, Avi Kivity wrote:
> > 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.
>
> I don't see why.
> I's about feature enablement, not feature discovery.

Well, "zero userspace coordination" would be a bug, since it would
remove userspace-controlled discovery. Since the userspace patches for
these types of features are usually very small, "less coordination"
doesn't buy us much.

> >
> > > * 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.
>
> Which structure? For msrs, we're usually going for just an u64, but of
> course we could change that when needed.

It's usually a physical address of a structure (together with an enable
bit).

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



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