Re: [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driverobjects

[Avi Kivity]

On 08/18/2009 01:28 PM, Michael S. Tsirkin wrote:
> > Suppose a nested guest has two devices.  One a virtual device backed by
> > its host (our guest), and one a virtual device backed by us (the real
> > host), and assigned by the guest to the nested guest.  If both devices
> > use hypercalls, there is no way to distinguish between them.
> >      
> Not sure I understand. What I had in mind is that devices would have to
> either use different hypercalls and map hypercall to address during
> setup, or pass address with each hypercall.  We get the hypercall,
> translate the address as if it was pio access, and know the destination?
>    

There are no different hypercalls.  There's just one hypercall 
instruction, and there's no standard on how it's used.  If a nested call 
issues a hypercall instruction, you have no idea if it's calling a 
Hyper-V hypercall or a vbus/virtio kick.

You could have a protocol where you register the hypercall instruction's 
address with its recipient, but it quickly becomes a tangled mess.  And 
for what?  pio and hypercalls have the same performance characteristics.

--
error compiling committee.c: too many arguments to function

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/