linux-kernel - [PATCH 2/2] vhost: set log when updating used flags or avail event

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Date:	Tue, 21 Jun 2011 18:04:38 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mst@...hat.com
Subject: [PATCH 2/2] vhost: set log when updating used flags or avail event

We need set log when updating used flags and avail event. Otherwise guest may
see stale values after migration and then do not exit or exit unexpectedly.

Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/vhost/vhost.c |   61 +++++++++++++++++++++++++++++++++++++++----------
 1 files changed, 48 insertions(+), 13 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 43a3fc6..c344d4f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -578,16 +578,6 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 	return 0;
 }
 
-int init_used(struct vhost_virtqueue *vq)
-{
-	int 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,
@@ -954,6 +944,51 @@ int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
 	return 0;
 }
 
+static int vhost_update_used_flags(struct vhost_virtqueue *vq)
+{
+	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. */
+		log_write(vq->log_base,
+			  vq->log_addr + offsetof(struct vring_used, flags),
+			  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)) {
+		/* Make sure the event is seen before log. */
+		smp_wmb();
+		/* Log avail event write */
+		log_write(vq->log_base,
+			  vq->log_addr + offsetof(struct vring_used,
+						  ring[vq->num]),
+			  sizeof avail_event);
+		if (vq->log_ctx)
+			eventfd_signal(vq->log_ctx, 1);
+	}
+	return 0;
+}
+
+int init_used(struct vhost_virtqueue *vq)
+{
+	int 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)
 {
@@ -1425,14 +1460,14 @@ 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);
@@ -1475,7 +1510,7 @@ 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);

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