[Qemu-devel] [PATCH v12 8/8] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ

[Wei Wang]

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 <address@hidden>
Signed-off-by: Liang Li <address@hidden>
---
 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) {
+               /*
+                * The VQ was full and kicked to release some descs. Now we
+                * will re-start to build the chain by using the hdr as the
+                * first desc, so we need to detach the desc that was just
+                * added, and re-start to add the hdr.
+                */
+               virtqueue_detach_buf(vb->cmd_vq, *head_id, NULL);
+               *head_id = VIRTQUEUE_DESC_ID_INIT;
+               *prev_id = VIRTQUEUE_DESC_ID_INIT;
+               goto retry;
+       }
+}
+
+static void cmdq_handle_stats(struct virtio_balloon *vb)
+{
+       unsigned int num_stats,
+                    head_id = VIRTQUEUE_DESC_ID_INIT,
+                    prev_id = VIRTQUEUE_DESC_ID_INIT;
+       uint64_t addr = (uint64_t)virt_to_phys((void *)vb->stats);
+       uint32_t len;
+
+       spin_lock(&vb->stop_update_lock);
+       if (!vb->stop_update) {
+               num_stats = update_balloon_stats(vb);
+               len = sizeof(struct virtio_balloon_stat) * num_stats;
+               cmdq_add_chain_desc(vb, &vb->cmdq_stats_hdr, addr, len,
+                                   &head_id, &prev_id);
+               virtqueue_add_chain(vb->cmd_vq, head_id, 0, NULL, vb, NULL);
+               virtqueue_kick_sync(vb->cmd_vq);
+       }
+       spin_unlock(&vb->stop_update_lock);
+}
+
+static void cmdq_add_unused_page(struct virtio_balloon *vb,
+                                struct zone *zone,
+                                unsigned int order,
+                                unsigned int type,
+                                struct page *page,
+                                unsigned int *head_id,
+                                unsigned int *prev_id)
+{
+       uint64_t addr;
+       uint32_t len;
+
+       while (!report_unused_page_block(zone, order, type, &page)) {
+               addr = (u64)page_to_pfn(page) << VIRTIO_BALLOON_PFN_SHIFT;
+               len = (u64)(1 << order) << VIRTIO_BALLOON_PFN_SHIFT;
+               cmdq_add_chain_desc(vb, &vb->cmdq_unused_page_hdr, addr, len,
+                                   head_id, prev_id);
+       }
+}
+
+static void cmdq_handle_unused_pages(struct virtio_balloon *vb)
+{
+       struct virtqueue *vq = vb->cmd_vq;
+       unsigned int order = 0, type = 0,
+                    head_id = VIRTQUEUE_DESC_ID_INIT,
+                    prev_id = VIRTQUEUE_DESC_ID_INIT;
+       struct zone *zone = NULL;
+       struct page *page = NULL;
+
+       for_each_populated_zone(zone)
+               for_each_migratetype_order(order, type)
+                       cmdq_add_unused_page(vb, zone, order, type, page,
+                                            &head_id, &prev_id);
+
+       /* Set the cmd completion flag. */
+       vb->cmdq_unused_page_hdr.flags |=
+                               cpu_to_le32(VIRTIO_BALLOON_CMDQ_F_COMPLETION);
+       virtqueue_add_chain(vq, head_id, 0, NULL, vb, NULL);
+       virtqueue_kick_sync(vb->cmd_vq);
+}
+
+static void cmdq_handle(struct virtio_balloon *vb)
+{
+       struct virtio_balloon_cmdq_hdr *hdr;
+       unsigned int len;
+
+       while ((hdr = (struct virtio_balloon_cmdq_hdr *)
+                       virtqueue_get_buf(vb->cmd_vq, &len)) != NULL) {
+               switch (__le32_to_cpu(hdr->cmd)) {
+               case VIRTIO_BALLOON_CMDQ_REPORT_STATS:
+                       cmdq_handle_stats(vb);
+                       break;
+               case VIRTIO_BALLOON_CMDQ_REPORT_UNUSED_PAGES:
+                       cmdq_handle_unused_pages(vb);
+                       break;
+               default:
+                       dev_warn(&vb->vdev->dev, "%s: wrong cmd\n", __func__);
+                       return;
+               }
+               /*
+                * Replenish all the command buffer to the device after a
+                * command is handled. This is for the convenience of the
+                * device to rewind the cmdq to get back all the command
+                * buffer after live migration.
+                */
+               cmdq_hdr_add(vb->cmd_vq, &vb->cmdq_stats_hdr, 1);
+               cmdq_hdr_add(vb->cmd_vq, &vb->cmdq_unused_page_hdr, 1);
+       }
+}
+
+static void cmdq_handle_work_func(struct work_struct *work)
+{
+       struct virtio_balloon *vb;
+
+       vb = container_of(work, struct virtio_balloon,
+                         cmdq_handle_work);
+       cmdq_handle(vb);
+}
+
+static void cmdq_callback(struct virtqueue *vq)
+{
+       struct virtio_balloon *vb = vq->vdev->priv;
+
+       queue_work(system_freezable_wq, &vb->cmdq_handle_work);
+}
+
 static int init_vqs(struct virtio_balloon *vb)
 {
-       struct virtqueue *vqs[3];
-       vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request 
};
-       static const char * const names[] = { "inflate", "deflate", "stats" };
-       int err, nvqs;
+       struct virtqueue **vqs;
+       vq_callback_t **callbacks;
+       const char **names;
+       int err = -ENOMEM;
+       int nvqs;
+
+       /* Inflateq and deflateq are used unconditionally */
+       nvqs = 2;
+
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_CMD_VQ) ||
+           virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ))
+               nvqs++;
+
+       /* Allocate space for find_vqs parameters */
+       vqs = kcalloc(nvqs, sizeof(*vqs), GFP_KERNEL);
+       if (!vqs)
+               goto err_vq;
+       callbacks = kmalloc_array(nvqs, sizeof(*callbacks), GFP_KERNEL);
+       if (!callbacks)
+               goto err_callback;
+       names = kmalloc_array(nvqs, sizeof(*names), GFP_KERNEL);
+       if (!names)
+               goto err_names;
+
+       callbacks[0] = balloon_ack;
+       names[0] = "inflate";
+       callbacks[1] = balloon_ack;
+       names[1] = "deflate";
 
        /*
-        * We expect two virtqueues: inflate and deflate, and
-        * optionally stat.
+        * The stats_vq is used only when cmdq is not supported (or disabled)
+        * by the device.
         */
-       nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
-       err = virtio_find_vqs(vb->vdev, nvqs, vqs, callbacks, names, NULL);
-       if (err)
-               return err;
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_CMD_VQ)) {
+               callbacks[2] = cmdq_callback;
+               names[2] = "cmdq";
+       } else if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
+               callbacks[2] = stats_request;
+               names[2] = "stats";
+       }
 
+       err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks,
+                                        names, NULL, NULL);
+       if (err)
+               goto err_find;
        vb->inflate_vq = vqs[0];
        vb->deflate_vq = vqs[1];
-       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
+
+       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_CMD_VQ)) {
+               vb->cmd_vq = vqs[2];
+               /* Prime the cmdq with the header buffer. */
+               cmdq_hdr_add(vb->cmd_vq, &vb->cmdq_stats_hdr, 1);
+               cmdq_hdr_add(vb->cmd_vq, &vb->cmdq_unused_page_hdr, 1);
+       } else if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
                struct scatterlist sg;
                unsigned int num_stats;
                vb->stats_vq = vqs[2];
@@ -520,6 +716,16 @@ static int init_vqs(struct virtio_balloon *vb)
                        BUG();
                virtqueue_kick(vb->stats_vq);
        }
+
+err_find:
+       kfree(names);
+err_names:
+       kfree(callbacks);
+err_callback:
+       kfree(vqs);
+err_vq:
+       return err;
+
        return 0;
 }
 
@@ -640,7 +846,18 @@ static int virtballoon_probe(struct virtio_device *vdev)
                goto out;
        }
 
-       INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
+       if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_CMD_VQ)) {
+               vb->cmdq_stats_hdr.cmd =
+                               cpu_to_le32(VIRTIO_BALLOON_CMDQ_REPORT_STATS);
+               vb->cmdq_stats_hdr.flags = 0;
+               vb->cmdq_unused_page_hdr.cmd =
+                       cpu_to_le32(VIRTIO_BALLOON_CMDQ_REPORT_UNUSED_PAGES);
+               vb->cmdq_unused_page_hdr.flags = 0;
+               INIT_WORK(&vb->cmdq_handle_work, cmdq_handle_work_func);
+       } else if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
+               INIT_WORK(&vb->update_balloon_stats_work,
+                         update_balloon_stats_func);
+       }
        INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
        spin_lock_init(&vb->stop_update_lock);
        vb->stop_update = false;
@@ -722,6 +939,7 @@ static void virtballoon_remove(struct virtio_device *vdev)
        spin_unlock_irq(&vb->stop_update_lock);
        cancel_work_sync(&vb->update_balloon_size_work);
        cancel_work_sync(&vb->update_balloon_stats_work);
+       cancel_work_sync(&vb->cmdq_handle_work);
 
        xb_empty(&vb->page_xb);
        remove_common(vb);
@@ -776,6 +994,7 @@ static unsigned int features[] = {
        VIRTIO_BALLOON_F_STATS_VQ,
        VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
        VIRTIO_BALLOON_F_SG,
+       VIRTIO_BALLOON_F_CMD_VQ,
 };
 
 static struct virtio_driver virtio_balloon_driver = {
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index b9d7e10..793de12 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -52,8 +52,13 @@
                        "%s:"fmt, (_vq)->vq.name, ##args);      \
                (_vq)->broken = true;                           \
        } while (0)
-#define START_USE(vq)
-#define END_USE(vq)
+#define START_USE(_vq)                                         \
+       do {                                                    \
+               while ((_vq)->in_use)                           \
+                       cpu_relax();                            \
+               (_vq)->in_use = __LINE__;                       \
+       } while (0)
+#define END_USE(_vq)   ((_vq)->in_use = 0)
 #endif
 
 struct vring_desc_state {
@@ -101,9 +106,9 @@ struct vring_virtqueue {
        size_t queue_size_in_bytes;
        dma_addr_t queue_dma_addr;
 
-#ifdef DEBUG
        /* They're supposed to lock for us. */
        unsigned int in_use;
+#ifdef DEBUG
 
        /* Figure out if their kicks are too delayed. */
        bool last_add_time_valid;
@@ -845,6 +850,18 @@ static void detach_buf(struct vring_virtqueue *vq, 
unsigned int head,
        }
 }
 
+void virtqueue_detach_buf(struct virtqueue *_vq, unsigned int head, void **ctx)
+{
+       struct vring_virtqueue *vq = to_vvq(_vq);
+
+       START_USE(vq);
+
+       detach_buf(vq, head, ctx);
+
+       END_USE(vq);
+}
+EXPORT_SYMBOL_GPL(virtqueue_detach_buf);
+
 static inline bool more_used(const struct vring_virtqueue *vq)
 {
        return vq->last_used_idx != virtio16_to_cpu(vq->vq.vdev, 
vq->vring.used->idx);
@@ -1158,8 +1175,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int 
index,
        vq->avail_idx_shadow = 0;
        vq->num_added = 0;
        list_add_tail(&vq->vq.list, &vdev->vqs);
+       vq->in_use = 0;
 #ifdef DEBUG
-       vq->in_use = false;
        vq->last_add_time_valid = false;
 #endif
 
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 9f27101..9df480b 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -88,6 +88,8 @@ void *virtqueue_get_buf(struct virtqueue *vq, unsigned int 
*len);
 void *virtqueue_get_buf_ctx(struct virtqueue *vq, unsigned int *len,
                            void **ctx);
 
+void virtqueue_detach_buf(struct virtqueue *_vq, unsigned int head, void 
**ctx);
+
 void virtqueue_disable_cb(struct virtqueue *vq);
 
 bool virtqueue_enable_cb(struct virtqueue *vq);
diff --git a/include/uapi/linux/virtio_balloon.h 
b/include/uapi/linux/virtio_balloon.h
index 37780a7..b38c370 100644
--- a/include/uapi/linux/virtio_balloon.h
+++ b/include/uapi/linux/virtio_balloon.h
@@ -35,6 +35,7 @@
 #define VIRTIO_BALLOON_F_STATS_VQ      1 /* Memory Stats virtqueue */
 #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM        2 /* Deflate balloon on OOM */
 #define VIRTIO_BALLOON_F_SG            3 /* Use sg instead of PFN lists */
+#define VIRTIO_BALLOON_F_CMD_VQ                4 /* Command virtqueue */
 
 /* Size of a PFN in the balloon interface. */
 #define VIRTIO_BALLOON_PFN_SHIFT 12
@@ -83,4 +84,13 @@ struct virtio_balloon_stat {
        __virtio64 val;
 } __attribute__((packed));
 
+struct virtio_balloon_cmdq_hdr {
+#define VIRTIO_BALLOON_CMDQ_REPORT_STATS       0
+#define VIRTIO_BALLOON_CMDQ_REPORT_UNUSED_PAGES        1
+       __le32 cmd;
+/* Flag to indicate the completion of handling a command */
+#define VIRTIO_BALLOON_CMDQ_F_COMPLETION       1
+       __le32 flags;
+};
+
 #endif /* _LINUX_VIRTIO_BALLOON_H */
-- 
2.7.4