On Mon, Dec 18, 2023 at 12:33 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 18.12.23 16:18, David Stevens wrote:
> > From: David Stevens <stevensd@xxxxxxxxxxxx>
> >
> > A virtio_balloon's parent device may be configured so that a
> > configuration change interrupt is a wakeup event. Extend the processing
> > of such a wakeup event until the balloon finishes inflating or deflating
> > by calling pm_stay_awake/pm_relax in the virtio_balloon driver. Note
> > that these calls are no-ops if the parent device doesn't support wakeup
> > events or if the wakeup events are not enabled.
> >
> > This change allows the guest to use system power states such as s2idle
> > without running the risk the virtio_balloon's cooperative memory
> > management becoming unresponsive to the host's requests.
> >
> > Signed-off-by: David Stevens <stevensd@xxxxxxxxxxxx>
> > ---
> > v1 -> v2:
> > - Use adjustment_signal_pending flag instead of a sequence number
> > - Call pm_stay_awake/pm_relax on parent device instead of adding a wake
> > event to the virtio balloon device
> >
> > drivers/virtio/virtio_balloon.c | 57 +++++++++++++++++++++++++++------
> > 1 file changed, 47 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> > index 1fe93e93f5bc..a3c11159cbe0 100644
> > --- a/drivers/virtio/virtio_balloon.c
> > +++ b/drivers/virtio/virtio_balloon.c
> > @@ -119,6 +119,11 @@ struct virtio_balloon {
> > /* Free page reporting device */
> > struct virtqueue *reporting_vq;
> > struct page_reporting_dev_info pr_dev_info;
> > +
> > + /* State for keeping the wakeup_source active while adjusting the balloon */
> > + spinlock_t adjustment_lock;
> > + bool adjustment_signal_pending;
> > + bool adjustment_in_progress;
> > };
> >
> > static const struct virtio_device_id id_table[] = {
> > @@ -437,6 +442,31 @@ static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb)
> > queue_work(vb->balloon_wq, &vb->report_free_page_work);
> > }
> >
> > +static void start_update_balloon_size(struct virtio_balloon *vb)
> > +{
> > + unsigned long flags;
> > +
> > + spin_lock_irqsave(&vb->adjustment_lock, flags);
> > + vb->adjustment_signal_pending = true;
> > + if (!vb->adjustment_in_progress) {
> > + vb->adjustment_in_progress = true;
> > + pm_stay_awake(vb->vdev->dev.parent);
> > + }
> > + spin_unlock_irqrestore(&vb->adjustment_lock, flags);
> > +
> > + queue_work(system_freezable_wq, &vb->update_balloon_size_work);
> > +}
> > +
> > +static void end_update_balloon_size(struct virtio_balloon *vb)
> > +{
> > + spin_lock(&vb->adjustment_lock);
> > + if (!vb->adjustment_signal_pending && vb->adjustment_in_progress) {
>
> How could vb->adjustment_in_progress ever not be set at this point?
>
> > + vb->adjustment_in_progress = false;
> > + pm_relax(vb->vdev->dev.parent);
> > + }
> > + spin_unlock(&vb->adjustment_lock);
> > +}
> > +
>
> LGTM, although I wonder what happens when calling pm_stay_awake() etc.
> on a parent device that is not wakeup-even-capable?
If the parent device is not wakeup capable or if wakeup isn't enabled,
then the vb->vdev->dev.parent->power.wakeup pointer will be NULL, so
the NULL checks in __pm_relax/__pm_stay_awake will immediately return.
-David
