vhost: set log when updating used flags or avail event

We need to log writes when updating used flags and avail event
fields.  Otherwise the guest may see a stale value after migration and
miss notifying the host.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 54 insertions, 30 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 9a108038fe5..46822c0d9f7 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -629,19 +629,6 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
         return 0;
 }
 
-int vhost_init_used(struct vhost_virtqueue *vq)
-{
-        int r;
-        if (!vq->private_data)
-                return 0;
-
-        r = put_user(vq->used_flags, &vq->used->flags);
-        if (r)
-                return r;
-        vq->signalled_used_valid = false;
-        return get_user(vq->last_used_idx, &vq->used->idx);
-}
-
 static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
 {
         struct file *eventfp, *filep = NULL,
@@ -1008,6 +995,57 @@ int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
         return 0;
 }
 
+static int vhost_update_used_flags(struct vhost_virtqueue *vq)
+{
+        void __user *used;
+        if (put_user(vq->used_flags, &vq->used->flags) < 0)
+                return -EFAULT;
+        if (unlikely(vq->log_used)) {
+                /* Make sure the flag is seen before log. */
+                smp_wmb();
+                /* Log used flag write. */
+                used = &vq->used->flags;
+                log_write(vq->log_base, vq->log_addr +
+                          (used - (void __user *)vq->used),
+                          sizeof vq->used->flags);
+                if (vq->log_ctx)
+                        eventfd_signal(vq->log_ctx, 1);
+        }
+        return 0;
+}
+
+static int vhost_update_avail_event(struct vhost_virtqueue *vq, u16 avail_event)
+{
+        if (put_user(vq->avail_idx, vhost_avail_event(vq)))
+                return -EFAULT;
+        if (unlikely(vq->log_used)) {
+                void __user *used;
+                /* Make sure the event is seen before log. */
+                smp_wmb();
+                /* Log avail event write */
+                used = vhost_avail_event(vq);
+                log_write(vq->log_base, vq->log_addr +
+                          (used - (void __user *)vq->used),
+                          sizeof *vhost_avail_event(vq));
+                if (vq->log_ctx)
+                        eventfd_signal(vq->log_ctx, 1);
+        }
+        return 0;
+}
+
+int vhost_init_used(struct vhost_virtqueue *vq)
+{
+        int r;
+        if (!vq->private_data)
+                return 0;
+
+        r = vhost_update_used_flags(vq);
+        if (r)
+                return r;
+        vq->signalled_used_valid = false;
+        return get_user(vq->last_used_idx, &vq->used->idx);
+}
+
 static int translate_desc(struct vhost_dev *dev, u64 addr, u32 len,
                           struct iovec iov[], int iov_size)
 {
@@ -1479,34 +1517,20 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
                 return false;
         vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
         if (!vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
-                r = put_user(vq->used_flags, &vq->used->flags);
+                r = vhost_update_used_flags(vq);
                 if (r) {
                         vq_err(vq, "Failed to enable notification at %p: %d\n",
                                &vq->used->flags, r);
                         return false;
                 }
         } else {
-                r = put_user(vq->avail_idx, vhost_avail_event(vq));
+                r = vhost_update_avail_event(vq, vq->avail_idx);
                 if (r) {
                         vq_err(vq, "Failed to update avail event index at %p: %d\n",
                                vhost_avail_event(vq), r);
                         return false;
                 }
         }
-        if (unlikely(vq->log_used)) {
-                void __user *used;
-                /* Make sure data is seen before log. */
-                smp_wmb();
-                used = vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX) ?
-                        &vq->used->flags : vhost_avail_event(vq);
-                /* Log used flags or event index entry write. Both are 16 bit
-                 * fields. */
-                log_write(vq->log_base, vq->log_addr +
-                           (used - (void __user *)vq->used),
-                          sizeof(u16));
-                if (vq->log_ctx)
-                        eventfd_signal(vq->log_ctx, 1);
-        }
         /* They could have slipped one in as we were doing that: make
          * sure it's written, then check again. */
         smp_mb();
@@ -1529,7 +1553,7 @@ void vhost_disable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
                 return;
         vq->used_flags |= VRING_USED_F_NO_NOTIFY;
         if (!vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
-                r = put_user(vq->used_flags, &vq->used->flags);
+                r = vhost_update_used_flags(vq);
                 if (r)
                         vq_err(vq, "Failed to enable notification at %p: %d\n",
                                &vq->used->flags, r);