[Xen-devel] RE: pvclock in userland (reprise)

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Keir Fraser wrote on Thu, 17 Sep 2009 at 12:03:42:

> On 17/09/2009 18:58, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>
> wrote:
> 
>> A remaining hard problem is that this single
>> "userland-accessible shared page" must be somehow
>> made available to apps (I suggested a rdmsr emulated
>> by Xen so that it works in userland) and must be
>> mapped into the app address space without kernel
>> changes.  I think someone (Keir?) suggested this
>> problem was solveable before we got sidetracked
>> on the need-vcpu-number-in-userland problem.
>  I don't think mapping things into application address space is really
> possible without guest kernel changes. The guest kernel owns and manages
> the pte that you'd be overwriting. Just blatting the pte would not be
> good form.
> 

Maybe you can write a device driver in the guest that sets up mapping against 
the (virtual) physical memory, then use mmap() in the app?

Jun
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Intel Open Source Technology Center




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