Xen devel - Jul 2008 - What are the mechanism for switching between Xen Hypervisor and Virtual Machine

Hello, everyone:
      I''m trying to summerize all the ways of control flow switch
between a
virtual machine and the Xen hypervisor, such as hypercall, either VM->Xen or
Xen->VM.
      Can you give me a complete list of all the ways and explain in general
them to some extent?
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>       I''m trying to summerize all the ways of control flow switch
between a
> virtual machine and the Xen hypervisor, such as hypercall, either
VM->Xen
> or Xen->VM.
>       Can you give me a complete list of all the ways and explain in
> general them to some extent?
VM->Xen transitions will occur on some some kind of interrupt-like event. 
For
instance, a software interrupt by the guest kernel (triggering a hypercall) 
and certain kinds of exceptions / faults that may occur whilst running the 
guest.  Interrupts from hardware devices - whether they''re owned by a
guest
or Xen itself - will also cause a guest->Xen transition so that Xen can take 
appropriate action.

Xen->VM transitions occur after Xen has handled an interrupt of some kind. 
If
the interrupt was handled internally by Xen, the guest may be unaware of 
this.  If a hypercall was being executed, the call will return in the guest.  
If Xen decided to send an event to a guest then the corresponding event 
channel bit will be set.  If Xen decided to reschedule then it may be 
returning to a *different* guest than when the interrupt occurred.

Hope that helps,
Cheers,
Mark


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