Re: [PATCH 0 of 3] Update paging/sharing/access interfaces v2

[Keir Fraser <keir.xen@gmail.com>]

On 10/02/2012 12:11, "Andres Lagar-Cavilla" <andres@lagarcavilla.org> wrote:

>>> I was just thinking about this issue. The bug is that the ring lives in
>>> dom0, the page should belong to domU and should be destroyed along with
>>> it. And ring users in dom0 should request (and maybe initially allocate
>>> and setup) a certain gfn belonging to domU.
>> 
>> Yes indeed. The gpfn could be allocated by the domain builder, or by
>> hvmloader (which might be too late!).
> 
> Well, let's say the domain builder reserves three gpfns (paging, access,
> sharing). When helpers for each come up, the enable domctl allocates the
> actual frame. Or, we could have the frames allocated up front, it's not
> terrible wastage -- the enable domctl would init the ring.
> 
> My question was more along the lines of how to choose which guest pfns to
> reserve for this.

Domain builder (xc_hvm_build.c) would be the sensible place to reserve, and
push that info down to Xen in some way. Then allocate the pages during the
enable domctl, via alloc_xenheap_page() (for a few arcane reasons, it's
better to use this than alloc_domheap_page() for this particular purpose).

 -- Keir