On Tue, Aug 07, 2018 at 05:52:12AM +1000, Benjamin Herrenschmidt wrote:

quoted

It is your job to write a coherent interface specification that does
not depend on the used components.  The hypervisor might be PAPR,
Linux + qemu, VMware, Hyperv or something so secret that you'd have
to shoot me if you had to tell me.  The guest might be Linux, FreeBSD,
AIX, OS400 or a Hipster project of the day in Rust.  As long as we
properly specify the interface it simplify does not matter.

That's the point Christoph. The interface is today's interface. It does
NOT change. That information is not part of the interface.

It's the VM itself that is stashing away its memory in a secret place,
and thus needs to do bounce buffering. There is no change to the virtio
interface per-se.

Any guest that doesn't know about your magic limited adressing is simply
not going to work, so we need to communicate that fact.