vhost: break out of polling loop on error

When ring parsing fails, we currently handle this
as ring empty condition. This means that we enable
kicks and recheck ring empty: if this not empty,
we re-start polling which of course will fail again.

Instead, let's return a negative error code and stop polling.

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

3 files changed, 31 insertions, 22 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 0f41c9195e9b..54096eef4840 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -98,7 +98,8 @@ static void tx_poll_start(struct vhost_net *net, struct socket *sock)
 static void handle_tx(struct vhost_net *net)
 {
         struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
-        unsigned head, out, in, s;
+        unsigned out, in, s;
+        int head;
         struct msghdr msg = {
                 .msg_name = NULL,
                 .msg_namelen = 0,
@@ -135,6 +136,9 @@ static void handle_tx(struct vhost_net *net)
                                          ARRAY_SIZE(vq->iov),
                                          &out, &in,
                                          NULL, NULL);
+                /* On error, stop handling until the next kick. */
+                if (head < 0)
+                        break;
                 /* Nothing new?  Wait for eventfd to tell us they refilled. */
                 if (head == vq->num) {
                         wmem = atomic_read(&sock->sk->sk_wmem_alloc);
@@ -192,7 +196,8 @@ static void handle_tx(struct vhost_net *net)
 static void handle_rx(struct vhost_net *net)
 {
         struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_RX];
-        unsigned head, out, in, log, s;
+        unsigned out, in, log, s;
+        int head;
         struct vhost_log *vq_log;
         struct msghdr msg = {
                 .msg_name = NULL,
@@ -228,6 +233,9 @@ static void handle_rx(struct vhost_net *net)
                                          ARRAY_SIZE(vq->iov),
                                          &out, &in,
                                          vq_log, &log);
+                /* On error, stop handling until the next kick. */
+                if (head < 0)
+                        break;
                 /* OK, now we need to know about added descriptors. */
                 if (head == vq->num) {
                         if (unlikely(vhost_enable_notify(vq))) {
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3b83382e06eb..5ccd384ec0be 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -873,12 +873,13 @@ static unsigned get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
  * number of output then some number of input descriptors, it's actually two
  * iovecs, but we pack them into one and note how many of each there were.
  *
- * This function returns the descriptor number found, or vq->num (which
- * is never a valid descriptor number) if none was found. */
-unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
-                           struct iovec iov[], unsigned int iov_size,
-                           unsigned int *out_num, unsigned int *in_num,
-                           struct vhost_log *log, unsigned int *log_num)
+ * This function returns the descriptor number found, or vq->num (which is
+ * never a valid descriptor number) if none was found.  A negative code is
+ * returned on error. */
+int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
+                      struct iovec iov[], unsigned int iov_size,
+                      unsigned int *out_num, unsigned int *in_num,
+                      struct vhost_log *log, unsigned int *log_num)
 {
         struct vring_desc desc;
         unsigned int i, head, found = 0;
@@ -890,13 +891,13 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
         if (get_user(vq->avail_idx, &vq->avail->idx)) {
                 vq_err(vq, "Failed to access avail idx at %p\n",
                        &vq->avail->idx);
-                return vq->num;
+                return -EFAULT;
         }
 
         if ((u16)(vq->avail_idx - last_avail_idx) > vq->num) {
                 vq_err(vq, "Guest moved used index from %u to %u",
                        last_avail_idx, vq->avail_idx);
-                return vq->num;
+                return -EFAULT;
         }
 
         /* If there's nothing new since last we looked, return invalid. */
@@ -912,14 +913,14 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
                 vq_err(vq, "Failed to read head: idx %d address %p\n",
                        last_avail_idx,
                        &vq->avail->ring[last_avail_idx % vq->num]);
-                return vq->num;
+                return -EFAULT;
         }
 
         /* If their number is silly, that's an error. */
         if (head >= vq->num) {
                 vq_err(vq, "Guest says index %u > %u is available",
                        head, vq->num);
-                return vq->num;
+                return -EINVAL;
         }
 
         /* When we start there are none of either input nor output. */
@@ -933,19 +934,19 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
                 if (i >= vq->num) {
                         vq_err(vq, "Desc index is %u > %u, head = %u",
                                i, vq->num, head);
-                        return vq->num;
+                        return -EINVAL;
                 }
                 if (++found > vq->num) {
                         vq_err(vq, "Loop detected: last one at %u "
                                "vq size %u head %u\n",
                                i, vq->num, head);
-                        return vq->num;
+                        return -EINVAL;
                 }
                 ret = copy_from_user(&desc, vq->desc + i, sizeof desc);
                 if (ret) {
                         vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
                                i, vq->desc + i);
-                        return vq->num;
+                        return -EFAULT;
                 }
                 if (desc.flags & VRING_DESC_F_INDIRECT) {
                         ret = get_indirect(dev, vq, iov, iov_size,
@@ -954,7 +955,7 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
                         if (ret < 0) {
                                 vq_err(vq, "Failure detected "
                                        "in indirect descriptor at idx %d\n", i);
-                                return vq->num;
+                                return ret;
                         }
                         continue;
                 }
@@ -964,7 +965,7 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
                 if (ret < 0) {
                         vq_err(vq, "Translation failure %d descriptor idx %d\n",
                                ret, i);
-                        return vq->num;
+                        return ret;
                 }
                 if (desc.flags & VRING_DESC_F_WRITE) {
                         /* If this is an input descriptor,
@@ -981,7 +982,7 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
                         if (*in_num) {
                                 vq_err(vq, "Descriptor has out after in: "
                                        "idx %d\n", i);
-                                return vq->num;
+                                return -EINVAL;
                         }
                         *out_num += ret;
                 }
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 44591ba9b07a..11ee13dba0f7 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -120,10 +120,10 @@ long vhost_dev_ioctl(struct vhost_dev *, unsigned int ioctl, unsigned long arg);
 int vhost_vq_access_ok(struct vhost_virtqueue *vq);
 int vhost_log_access_ok(struct vhost_dev *);
 
-unsigned vhost_get_vq_desc(struct vhost_dev *, struct vhost_virtqueue *,
-                           struct iovec iov[], unsigned int iov_count,
-                           unsigned int *out_num, unsigned int *in_num,
-                           struct vhost_log *log, unsigned int *log_num);
+int vhost_get_vq_desc(struct vhost_dev *, struct vhost_virtqueue *,
+                      struct iovec iov[], unsigned int iov_count,
+                      unsigned int *out_num, unsigned int *in_num,
+                      struct vhost_log *log, unsigned int *log_num);
 void vhost_discard_vq_desc(struct vhost_virtqueue *);
 
 int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);