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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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?

Jan


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