Re: Device model architecture (Was Re: [Xen-devel] Re: Are linkerscripts needed?)

[Arun Sharma <arun.sharma@xxxxxxxxx>]

Ian Pratt wrote:
>  > > When switching between the vmcs guest and the minios, we 
>
> > just need to 
> >
> > > switch new values into the guest_table variable and the shadow_mode 
> > > variable and then all the Xen logic will do the right 
> > thing. (no cr3 
> >
> > > flush in incurred)
> > I guess the main logic behind your argument is that there is 
> > no need to fully virtualize the device models, so no need to 
> > run them within a non-root VMCS.
>
> We can't run them in the same non-root VMCS as the guest since we need
> some virtual address space. Since the hardware does a cr3 switch to the
> monitor_table when doing a vmexit, wwe might as well make better use of
> this and treat the device models as just another paravirtualized guest.
>  
I thought some more about this. We can't think of device models as a 
bunch of code that run only during a vmexit. It needs to be able to 
handle asynchronous events such as keyboard/mouse input or other sources 
of events and inject interrupts into the VMX domain ASAP.
Specifically, on a dual CPU system or a HT system, we should be able to 
run device models on one CPU and the VMX domains on another CPU. This is 
possible in the current design.
        -Arun

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