Re: [Xen-devel] [PATCH 6/8] xen/pvh: Initialize grant table for PVH guests
From: Juergen Gross
Date: Tue Oct 18 2016 - 12:08:52 EST
On 14/10/16 22:02, Boris Ostrovsky wrote:
> On 10/14/2016 03:51 PM, Konrad Rzeszutek Wilk wrote:
>> On Fri, Oct 14, 2016 at 03:43:19PM -0400, Boris Ostrovsky wrote:
>>> On 10/14/2016 03:19 PM, Konrad Rzeszutek Wilk wrote:
>>>> On Fri, Oct 14, 2016 at 02:05:16PM -0400, Boris Ostrovsky wrote:
>>>> Perhaps add in here:
>>>> PVH is like PV in that there are no PCI devices - which HVM
>>>> code would piggyback on to find the Xen PCI platform device and
>>>> use its MMIO space to stash the grants in.
>>>> For PVH we balloon out memory and stash the grants in there.
>>>> (Which begs the next question - where and when do we balloon out the
>>>> normal memory back in?)
>>> Are you saying that we should get back memory that we gave to grant tables?
>> In pure HVM that area is MMIO - which hvmloader has balloonned out.
>> The hvmloader then balloons that number of pages back at the end of
>> guest memory (after 4GB).
> We don't do this for PV though, do we?
Uuh, kind of. We try to allocate granted pages from the ballooned area.
So for PV(H) we don't need to balloon this memory back in as it was
never shadowed by a grant.