Re: [Xen-devel] [PATCH for-4.6] xen/mm: populate_physmap: validate correctly the gfn for direct mapped domain

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Thu, 2015-08-13 at 04:29 -0600, Jan Beulich wrote:
> > 
> > > > On 13.08.15 at 12:14, <ian.campbell@xxxxxxxxxx> wrote:
> > There isn't a race here is there? What if the reference were dropped 
> > after
> > this check but before the guest_physmap_add_page (which takes new
> > references)? We are implicitly relying on a guarantee made elsewhere 
> > that a
> > direct mapped guest never drops the final ref until it is destroyed 
> > (which
> > can't be happening in this window I think), but it would be obviously 
> > safer
> > against such bugs if we just held the ref until after the p2m was 
> > updated.
> 
> Yeah, we depend on this, and what you suggest would indeed be
> an improvment.
> 
> > Another thing for a future/4.7 cleanup I guess.
> 
> Right.
> 
> But as bottom line I take it that your objections to the patch going in
> soon have been eliminated?

Correct.

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>


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