Re: [Qemu-devel] [Xen-devel] [PATCH v3 5/6] xen: record physmap changes to xenstore

[Stefano Stabellini]

On Thu, 19 Jan 2012, Ian Campbell wrote:
> On Thu, 2012-01-19 at 11:56 +0000, Stefano Stabellini wrote:
> > Write to xenstore any physmap changes so that the hypervisor can be
> > aware of them.
> 
> What is the structure of the xenstore values? Looks like 
>       <domid>/physmap/<original-addr>/start_addr <new-addr>
> ?

Yep, that is the structure


> Who defines the meaning of original-addr, in particular what happens
> if it the original-addr for a device changes in a N->N+1 migration? What
> happens if things overlap or if a subsequent call only updates part of a
> previously moved mapping?

In practice it cannot happen because on restore Qemu is going to emulate
the same set of devices it was emulating before.
The original address is not going to change if the devices and the
amount of guest memory stay the same.

We could add some additional info to better identify the physmap entry,
probably the best we could use is the memory_region name.