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From:   David Stevens <stevensd@chromium.org>
To:     "Michael S . Tsirkin" <mst@redhat.com>,
        David Hildenbrand <david@redhat.com>
Cc:     virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, David Stevens <stevensd@chromium.org>
Subject: [PATCH] virtio_balloon: stay awake while adjusting balloon
Date:   Mon, 11 Dec 2023 20:43:46 +0900
Message-ID: <20231211114346.1132386-1-stevensd@google.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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From: David Stevens <stevensd@chromium.org>

Add a wakeup event for when the balloon is inflating or deflating.
Userspace can enable this wakeup event to prevent the system from
suspending while the balloon is being adjusted. This allows
/sys/power/wakeup_count to be used without breaking virtio_balloon's
cooperative memory management.

Signed-off-by: David Stevens <stevensd@chromium.org>
---
 drivers/virtio/virtio_balloon.c | 59 +++++++++++++++++++++++++++------
 1 file changed, 49 insertions(+), 10 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 1fe93e93f5bc..811d8937246a 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;
+	u32 adjustment_seqno;
+	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_seqno++;
+	if (!vb->adjustment_in_progress) {
+		vb->adjustment_in_progress = true;
+		pm_stay_awake(&vb->vdev->dev);
+	}
+	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, u32 seqno)
+{
+	spin_lock(&vb->adjustment_lock);
+	if (vb->adjustment_seqno == seqno && vb->adjustment_in_progress) {
+		vb->adjustment_in_progress = false;
+		pm_relax(&vb->vdev->dev);
+	}
+	spin_unlock(&vb->adjustment_lock);
+}
+
 static void virtballoon_changed(struct virtio_device *vdev)
 {
 	struct virtio_balloon *vb = vdev->priv;
@@ -444,8 +474,7 @@ static void virtballoon_changed(struct virtio_device *vdev)
 
 	spin_lock_irqsave(&vb->stop_update_lock, flags);
 	if (!vb->stop_update) {
-		queue_work(system_freezable_wq,
-			   &vb->update_balloon_size_work);
+		start_update_balloon_size(vb);
 		virtio_balloon_queue_free_page_work(vb);
 	}
 	spin_unlock_irqrestore(&vb->stop_update_lock, flags);
@@ -473,22 +502,29 @@ static void update_balloon_size_func(struct work_struct *work)
 {
 	struct virtio_balloon *vb;
 	s64 diff;
+	u32 seqno;
 
 	vb = container_of(work, struct virtio_balloon,
 			  update_balloon_size_work);
-	diff = towards_target(vb);
 
-	if (!diff)
-		return;
+	spin_lock(&vb->adjustment_lock);
+	seqno = vb->adjustment_seqno;
+	spin_unlock(&vb->adjustment_lock);
 
-	if (diff > 0)
-		diff -= fill_balloon(vb, diff);
-	else
-		diff += leak_balloon(vb, -diff);
-	update_balloon_size(vb);
+	diff = towards_target(vb);
+
+	if (diff) {
+		if (diff > 0)
+			diff -= fill_balloon(vb, diff);
+		else
+			diff += leak_balloon(vb, -diff);
+		update_balloon_size(vb);
+	}
 
 	if (diff)
 		queue_work(system_freezable_wq, work);
+	else
+		end_update_balloon_size(vb, seqno);
 }
 
 static int init_vqs(struct virtio_balloon *vb)
@@ -992,6 +1028,9 @@ static int virtballoon_probe(struct virtio_device *vdev)
 			goto out_unregister_oom;
 	}
 
+	spin_lock_init(&vb->adjustment_lock);
+	device_set_wakeup_capable(&vb->vdev->dev, true);
+
 	virtio_device_ready(vdev);
 
 	if (towards_target(vb))
-- 
2.43.0.472.g3155946c3a-goog