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    SubjectRe: [Xen-devel] [PATCH 6/8] xen/pvh: Initialize grant table for PVH guests
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    On 10/18/2016 12:08 PM, Juergen Gross wrote:
    > 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?
    >>> 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?
    > Uuh, kind of. We try to allocate granted pages from the ballooned area.
    > See gnttab_alloc_pages().


    I meant that we don't give memory back for PV.


    >
    > So for PV(H) we don't need to balloon this memory back in as it was
    > never shadowed by a grant.


    Is it *never* or *may or may not be* shadowed? (I assume "shadowed"
    means "used for" here.)

    -boris

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