Accessing the hypervisor from VMs

Accessing the hypervisor from VMs

[Diwaker Gupta]

Hi everyone,

Is it possible to access the hypervisor through a VM other than dom0?
I'm not interested in all the control functions -- lets just say I
want to access the value of some hypervisor variable (stime_irq, for
instance) from a guest.

TIA
-- 
Diwaker Gupta
http://resolute.ucsd.edu/diwaker


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Re: Accessing the hypervisor from VMs

[Mark Williamson]

You could add one or more hypercalls to do this.  Alternatively, you can put 
the information you want to pass up into a shared memory page so that dom0 
can read it directly.

Cheers,
Mark

On Wednesday 09 March 2005 19:31, Diwaker Gupta wrote:
> Hi everyone,
>
> Is it possible to access the hypervisor through a VM other than dom0?
> I'm not interested in all the control functions -- lets just say I
> want to access the value of some hypervisor variable (stime_irq, for
> instance) from a guest.
>
> TIA


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Re: Accessing the hypervisor from VMs

[Diwaker Gupta]

> You could add one or more hypercalls to do this.  Alternatively, you can put
> the information you want to pass up into a shared memory page so that dom0
> can read it directly.

> > Is it possible to access the hypervisor through a VM other than dom0?

Sure, I can do all this from dom0, but I want to be able to do it from
guests other than dom0 -- how does that work?
-- 
Diwaker Gupta
http://resolute.ucsd.edu/diwaker


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Re: Accessing the hypervisor from VMs

[Mark Williamson]

On Wednesday 09 March 2005 21:17, Diwaker Gupta wrote:
> > You could add one or more hypercalls to do this.  Alternatively, you can
> > put the information you want to pass up into a shared memory page so that
> > dom0 can read it directly.
> >
> > > Is it possible to access the hypervisor through a VM other than dom0?
>
> Sure, I can do all this from dom0, but I want to be able to do it from
> guests other than dom0 -- how does that work?

You could add a new type of hypercall that is available to any dom and returns 
the data you require.  For starters, take a look at the hypercall table in 
xen/arch/x86/x86_32/entry.S

All you need to do to make it work with unpriv domains is to not check the 
domains privileges ;-)

Setting up Xen <-> domU shared memory would be a bit more involved.

Cheers,
Mark


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