Messages in this thread | | | Date | Wed, 26 Jan 2011 17:17:02 +0200 | From | Avi Kivity <> | Subject | Re: [PATCH 05/16] KVM-HDR: Implement wallclock over KVM - KVM Virtual Memory |
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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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