RE: [Xen-devel] Strange (???) xl behavior for save, migrate and migrate-receive

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Daniel Kiper [mailto:dkiper@xxxxxxxxxxxx]
> Subject: Re: [Xen-devel] Strange (???) xl behavior for save, migrate and 
> migrate-receive
> 
> On Tue, Oct 18, 2011 at 09:19:01AM +0100, Ian Campbell wrote:
> > On Mon, 2011-10-17 at 19:44 +0100, Dan Magenheimer wrote:
> > > In a recent internal discussion at Oracle, we were thinking about
> > > whether to enable hotplug functionality in a guest kernel and it
> > > raised some concerns about manageability.  I think right now
> > > the system administrator of the guest can arbitrarily increase
> > > memory size beyond maxmem...
> >
> > The memory limit for a guest is ultimately controlled by the host
> > administrator/toolstack. The in-guest admin cannot exceed that, even
> > using hotplug.
> 
> Correct.
> 
> > I think that limit is currently always set to the current balloon target.
> 
> Nope. It is set by maxmem option.
> 
> > AIUI Daniel's work only allows a guest admin to take advantage of new
> > memory above maxmem _after_ the host admin has provisioned that RAM to
> > the guest. IOW it only allows the guest to take advantage of new memory
> > given to it and does not allow the guest to acquire new memory of its
> > own accord.
> 
> Guest/host administartor could allocate for given guest no more memory than
> maxmem (its value could be changed by xl mem-max <domain> <new_size>) allows,
> regardless of mechanism (ballooning or memory hotplug) used for that 
> allocation.
> It means that memory hotplug does not pose any security threat in that area.

OK, thanks for the clarification, Daniel and Ian.

> > P.S. Also FYI, selfballooning is implemented in Oracle's kernel
> > so we should work to ensure that selfballooning and hotplug
> > work properly together.
> 
> I am happy to do that, however, I am very busy now.
> Could we postpone this 2-3 months ???

Sure, that's fine.

Dan

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