Re: [Xen-devel] libxl/xl memory paging/sharing/ballooning/etc proposal.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-03-15 at 15:42 +0000, Olaf Hering wrote:
> On Thu, Mar 15, Ian Campbell wrote:
> 
> > On Thu, 2012-03-15 at 15:26 +0000, Olaf Hering wrote:
> > > On Thu, Mar 15, Andres Lagar-Cavilla wrote:
> > > 
> > > 
> > > > > libxl_domain_(set|get)_paging_target(ctx, domid, target_memkb, 
> > > > > relative)
> > > > >
> > > > >         Read/write whichever XS path controls the xenpaging daemon's
> > > > >         target. (Olaf?). I think this path should not be
> > > > >         under /local/domain since it should not be guest visible
> > > > >         (probably it already isn't).
> > > > It is /local/domain/X/memory/target-tot_pages. I agree it should not be
> > > > guest visible, and we're still in time to change it.
> > > 
> > > Is it guest visible? I think the entry point for a guest is /vm/<uuid>/,
> > > I'm almost sure it can not get to /local/domain/X/memory/
> > 
> > /local/domain/X is generally considered to be part of the "guest
> > visible" state and there are various guest visible things there,
> > devices/* and memory/target spring to mind.
> 
> Is memory/target below /local/domain/X or /vm/<uuid> in use by the guet?

/local/domain/X. The is no such key under /vm/<uuid>

> I'm sure the latter can only be used to set a watch for example (dont
> have a guest at hand to verify).
> Also the guest would have to proactivly parse the "links" to find its
> domid, to later browse /local/domain/X.

No, /local/domain/X is the domains "home directory", it is what relative
paths are relative to -- so to access /local/domain/X/memory/target a
domain just accesses "memory/target"

> What would it protect if /local/domain/X/memory (and other parts) are not 
> accesible?

XS has a permissions scheme which allows per domain r/w, r/o or none.

Something like the paging target should not even be r/o for the guest
IMHO. In general we try to keep stuff which the domain should not even
be looking at separate from the stuff which it should.

Ian.


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