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

[Ian Campbell]

On Thu, 2012-01-19 at 13:08 +0000, Stefano Stabellini wrote:
> 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.

If you are migrating to a newer qemu then the <original-addr> could in
principal change, I think.

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

And/Or the PCI BDF + BAR?

Ian.