linux-kernel - Re: [Xen-devel] [PATCH 6/8] xen/pvh: Initialize grant table for PVH guests

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Date:   Fri, 14 Oct 2016 16:02:52 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     david.vrabel@...rix.com, JGross@...e.com,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        roger.pau@...rix.com
Subject: Re: [Xen-devel] [PATCH 6/8] xen/pvh: Initialize grant table for PVH
 guests

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?
> Yes.
>
> 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?

-boris