On 07/13/2017 08:22 AM, Michael S. Tsirkin wrote:

On Wed, Jul 12, 2017 at 08:40:21PM +0800, Wei Wang wrote:

quoted

Add a new vq, cmdq, to handle requests between the device and driver.

This patch implements two commands sent from the device and handled in
the driver.
1) VIRTIO_BALLOON_CMDQ_REPORT_STATS: this command is used to report
the guest memory statistics to the host. The stats_vq mechanism is not
used when the cmdq mechanism is enabled.
2) VIRTIO_BALLOON_CMDQ_REPORT_UNUSED_PAGES: this command is used to
report the guest unused pages to the host.

Since now we have a vq to handle multiple commands, we need to keep only
one vq operation at a time. Here, we change the existing START_USE()
and END_USE() to lock on each vq operation.

Signed-off-by: Wei Wang <redacted>
Signed-off-by: Liang Li <redacted>
---
  drivers/virtio/virtio_balloon.c     | 245 ++++++++++++++++++++++++++++++++++--
  drivers/virtio/virtio_ring.c        |  25 +++-
  include/linux/virtio.h              |   2 +
  include/uapi/linux/virtio_balloon.h |  10 ++
  4 files changed, 265 insertions(+), 17 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index aa4e7ec..ae91fbf 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c

@@ -54,11 +54,12 @@ static struct vfsmount *balloon_mnt;
  
  struct virtio_balloon {
  	struct virtio_device *vdev;
-	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
+	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *cmd_vq;
  
  	/* The balloon servicing is delegated to a freezable workqueue. */
  	struct work_struct update_balloon_stats_work;
  	struct work_struct update_balloon_size_work;
+	struct work_struct cmdq_handle_work;
  
  	/* Prevent updating balloon when it is being canceled. */
  	spinlock_t stop_update_lock;

@@ -90,6 +91,12 @@ struct virtio_balloon {
  	/* Memory statistics */
  	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
  
+	/* Cmdq msg buffer for memory statistics */
+	struct virtio_balloon_cmdq_hdr cmdq_stats_hdr;
+
+	/* Cmdq msg buffer for reporting ununsed pages */
+	struct virtio_balloon_cmdq_hdr cmdq_unused_page_hdr;
+
  	/* To register callback in oom notifier call chain */
  	struct notifier_block nb;
  };

@@ -485,25 +492,214 @@ static void update_balloon_size_func(struct work_struct *work)
  		queue_work(system_freezable_wq, work);
  }
  
+static unsigned int cmdq_hdr_add(struct virtqueue *vq,
+				 struct virtio_balloon_cmdq_hdr *hdr,
+				 bool in)
+{
+	unsigned int id = VIRTQUEUE_DESC_ID_INIT;
+	uint64_t hdr_pa = (uint64_t)virt_to_phys((void *)hdr);
+
+	virtqueue_add_chain_desc(vq, hdr_pa, sizeof(*hdr), &id, &id, in);
+
+	/* Deliver the hdr for the host to send commands. */
+	if (in) {
+		hdr->flags = 0;
+		virtqueue_add_chain(vq, id, 0, NULL, hdr, NULL);
+		virtqueue_kick(vq);
+	}
+
+	return id;
+}
+
+static void cmdq_add_chain_desc(struct virtio_balloon *vb,
+				struct virtio_balloon_cmdq_hdr *hdr,
+				uint64_t addr,
+				uint32_t len,
+				unsigned int *head_id,
+				unsigned int *prev_id)
+{
+retry:
+	if (*head_id == VIRTQUEUE_DESC_ID_INIT) {
+		*head_id = cmdq_hdr_add(vb->cmd_vq, hdr, 0);
+		*prev_id = *head_id;
+	}
+
+	virtqueue_add_chain_desc(vb->cmd_vq, addr, len, head_id, prev_id, 0);
+	if (*head_id == *prev_id) {

That's an ugly way to detect ring full.

It's actually not detecting ring full. I will call it tail_id, instead 
of prev_id.
So, *head_id == *tail_id is the case that the first desc was just added by
  virtqueue_add_chain_desc().

Best,
Wei

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