On Wed, 5 Dec 2018 17:38:22 +0100
David Hildenbrand <da...@redhat.com> wrote:
> On 05.12.18 15:51, Cornelia Huck wrote:
> > vfio-ap devices do not pin any pages in the host. Therefore, they
> > are belived to be compatible with memory ballooning.
> >
> > Flag them as compatible, so both vfio-ap and a balloon can be
> > used simultaneously.
> >
> > Signed-off-by: Cornelia Huck <coh...@redhat.com>
> > ---
> >
> > As briefly discussed on IRC. RFC as I do not have easy access to
> > hardware I can test this with.
> >
> > ---
> > hw/vfio/ap.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/hw/vfio/ap.c b/hw/vfio/ap.c
> > index 65de952f44..3bf48eed28 100644
> > --- a/hw/vfio/ap.c
> > +++ b/hw/vfio/ap.c
> > @@ -104,6 +104,14 @@ static void vfio_ap_realize(DeviceState *dev, Error
> > **errp)
> > vapdev->vdev.name = g_strdup_printf("%s", mdevid);
> > vapdev->vdev.dev = dev;
> >
> > + /*
> > + * vfio-ap devices are believed to operate in a way compatible with
> > + * memory ballooning, as no pages are pinned in the host.
> > + * This needs to be set before vfio_get_device() for vfio common to
> > + * handle the balloon inhibitor.
> > + */
> > + vapdev->vdev.balloon_allowed = true;
> > +
> > ret = vfio_get_device(vfio_group, mdevid, &vapdev->vdev, &local_err);
> > if (ret) {
> > goto out_get_dev_err;
> >
>
> What happens if this ever changes? Shouldn't we have an API to at least
> check what the vfio device can guarantee?
>
> "are believed to operate" doesn't sound like guarantees to me :)
It's the same for ccw :)
While such an API definitely sounds like a good idea, it is probably
overkill to introduce it for this case (do we envision changing the way
vfio-ap operates in the future to make that statement non-true?)
