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

[Arun Sharma <arun.sharma@xxxxxxxxx>]

Ian Pratt wrote:
> I'd be inclined to move to a model where we execute the device emulation
> in the root (monitor) VMCS, using the same protection mechanism we use
> for para-virtualized guests e.g. segmentation for x86, paging for
> x86_64. The device emulation should should work like a normal front-end
> driver, connecting via a device channel to a normal backend.
It sounded like you were proposing linking the device models against 
Xen. But your subsequent messages appear to say:
- For every VMX domain created, create a new helper domain
- The helper domain shares it's page list with the VMX domain
- xen is protected from the helper domain using paging/segmentation
- helper domain runs minios
- Use the existing mechanisms (backend drivers) to get storage/network 
services from dom0
Did I get it right? If yes,

- why is this better than running the device models inside the VMX 
domain? Do you expect switching to the helper domain to be faster than a 
 vmx world switch?
- what's the advantage of running minios vs xenolinux in the helper domain?

I think we all agree that:

- It'd be good to make the device models "embeddable" so that it could 
be moved closer to the domain it's servicing. This is where the bulk of 
the work is, regardless of which model we end up choosing.
- Make sure that there is a unified way to manage the resources given to 
the VMX domain (including the device models)
        -Arun

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