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Message-ID: <20251113015420.3496-1-jasowang@redhat.com>
Date: Thu, 13 Nov 2025 09:54:20 +0800
From: Jason Wang <jasowang@...hat.com>
To: mst@...hat.com,
kvm@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: Jason Wang <jasowang@...hat.com>,
stable@...r.kernel.org
Subject: [PATCH net] vhost: rewind next_avail_head while discarding descriptors
When discarding descriptors with IN_ORDER, we should rewind
next_avail_head otherwise it would run out of sync with
last_avail_idx. This would cause driver to report
"id X is not a head".
Fixing this by returning the number of descriptors that is used for
each buffer via vhost_get_vq_desc_n() so caller can use the value
while discarding descriptors.
Fixes: 67a873df0c41 ("vhost: basic in order support")
Cc: stable@...r.kernel.org
Signed-off-by: Jason Wang <jasowang@...hat.com>
---
drivers/vhost/net.c | 53 ++++++++++++++++++++++++++-----------------
drivers/vhost/vhost.c | 43 ++++++++++++++++++++++++-----------
drivers/vhost/vhost.h | 9 +++++++-
3 files changed, 70 insertions(+), 35 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 35ded4330431..8f7f50acb6d6 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -592,14 +592,15 @@ static void vhost_net_busy_poll(struct vhost_net *net,
static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
struct vhost_net_virtqueue *tnvq,
unsigned int *out_num, unsigned int *in_num,
- struct msghdr *msghdr, bool *busyloop_intr)
+ struct msghdr *msghdr, bool *busyloop_intr,
+ unsigned int *ndesc)
{
struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
struct vhost_virtqueue *rvq = &rnvq->vq;
struct vhost_virtqueue *tvq = &tnvq->vq;
- int r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
- out_num, in_num, NULL, NULL);
+ int r = vhost_get_vq_desc_n(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
+ out_num, in_num, NULL, NULL, ndesc);
if (r == tvq->num && tvq->busyloop_timeout) {
/* Flush batched packets first */
@@ -610,8 +611,8 @@ static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, false);
- r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
- out_num, in_num, NULL, NULL);
+ r = vhost_get_vq_desc_n(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
+ out_num, in_num, NULL, NULL, ndesc);
}
return r;
@@ -642,12 +643,14 @@ static int get_tx_bufs(struct vhost_net *net,
struct vhost_net_virtqueue *nvq,
struct msghdr *msg,
unsigned int *out, unsigned int *in,
- size_t *len, bool *busyloop_intr)
+ size_t *len, bool *busyloop_intr,
+ unsigned int *ndesc)
{
struct vhost_virtqueue *vq = &nvq->vq;
int ret;
- ret = vhost_net_tx_get_vq_desc(net, nvq, out, in, msg, busyloop_intr);
+ ret = vhost_net_tx_get_vq_desc(net, nvq, out, in, msg,
+ busyloop_intr, ndesc);
if (ret < 0 || ret == vq->num)
return ret;
@@ -766,6 +769,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
int sent_pkts = 0;
bool sock_can_batch = (sock->sk->sk_sndbuf == INT_MAX);
bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER);
+ unsigned int ndesc = 0;
do {
bool busyloop_intr = false;
@@ -774,7 +778,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
vhost_tx_batch(net, nvq, sock, &msg);
head = get_tx_bufs(net, nvq, &msg, &out, &in, &len,
- &busyloop_intr);
+ &busyloop_intr, &ndesc);
/* On error, stop handling until the next kick. */
if (unlikely(head < 0))
break;
@@ -806,7 +810,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
goto done;
} else if (unlikely(err != -ENOSPC)) {
vhost_tx_batch(net, nvq, sock, &msg);
- vhost_discard_vq_desc(vq, 1);
+ vhost_discard_vq_desc(vq, 1, ndesc);
vhost_net_enable_vq(net, vq);
break;
}
@@ -829,7 +833,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
err = sock->ops->sendmsg(sock, &msg, len);
if (unlikely(err < 0)) {
if (err == -EAGAIN || err == -ENOMEM || err == -ENOBUFS) {
- vhost_discard_vq_desc(vq, 1);
+ vhost_discard_vq_desc(vq, 1, ndesc);
vhost_net_enable_vq(net, vq);
break;
}
@@ -868,6 +872,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
int err;
struct vhost_net_ubuf_ref *ubufs;
struct ubuf_info_msgzc *ubuf;
+ unsigned int ndesc = 0;
bool zcopy_used;
int sent_pkts = 0;
@@ -879,7 +884,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
busyloop_intr = false;
head = get_tx_bufs(net, nvq, &msg, &out, &in, &len,
- &busyloop_intr);
+ &busyloop_intr, &ndesc);
/* On error, stop handling until the next kick. */
if (unlikely(head < 0))
break;
@@ -941,7 +946,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
vq->heads[ubuf->desc].len = VHOST_DMA_DONE_LEN;
}
if (retry) {
- vhost_discard_vq_desc(vq, 1);
+ vhost_discard_vq_desc(vq, 1, ndesc);
vhost_net_enable_vq(net, vq);
break;
}
@@ -1045,11 +1050,12 @@ static int get_rx_bufs(struct vhost_net_virtqueue *nvq,
unsigned *iovcount,
struct vhost_log *log,
unsigned *log_num,
- unsigned int quota)
+ unsigned int quota,
+ unsigned int *ndesc)
{
struct vhost_virtqueue *vq = &nvq->vq;
bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER);
- unsigned int out, in;
+ unsigned int out, in, desc_num, n = 0;
int seg = 0;
int headcount = 0;
unsigned d;
@@ -1064,9 +1070,9 @@ static int get_rx_bufs(struct vhost_net_virtqueue *nvq,
r = -ENOBUFS;
goto err;
}
- r = vhost_get_vq_desc(vq, vq->iov + seg,
- ARRAY_SIZE(vq->iov) - seg, &out,
- &in, log, log_num);
+ r = vhost_get_vq_desc_n(vq, vq->iov + seg,
+ ARRAY_SIZE(vq->iov) - seg, &out,
+ &in, log, log_num, &desc_num);
if (unlikely(r < 0))
goto err;
@@ -1093,6 +1099,7 @@ static int get_rx_bufs(struct vhost_net_virtqueue *nvq,
++headcount;
datalen -= len;
seg += in;
+ n += desc_num;
}
*iovcount = seg;
@@ -1113,9 +1120,11 @@ static int get_rx_bufs(struct vhost_net_virtqueue *nvq,
nheads[0] = headcount;
}
+ *ndesc = n;
+
return headcount;
err:
- vhost_discard_vq_desc(vq, headcount);
+ vhost_discard_vq_desc(vq, headcount, n);
return r;
}
@@ -1151,6 +1160,7 @@ static void handle_rx(struct vhost_net *net)
struct iov_iter fixup;
__virtio16 num_buffers;
int recv_pkts = 0;
+ unsigned int ndesc;
mutex_lock_nested(&vq->mutex, VHOST_NET_VQ_RX);
sock = vhost_vq_get_backend(vq);
@@ -1182,7 +1192,8 @@ static void handle_rx(struct vhost_net *net)
headcount = get_rx_bufs(nvq, vq->heads + count,
vq->nheads + count,
vhost_len, &in, vq_log, &log,
- likely(mergeable) ? UIO_MAXIOV : 1);
+ likely(mergeable) ? UIO_MAXIOV : 1,
+ &ndesc);
/* On error, stop handling until the next kick. */
if (unlikely(headcount < 0))
goto out;
@@ -1228,7 +1239,7 @@ static void handle_rx(struct vhost_net *net)
if (unlikely(err != sock_len)) {
pr_debug("Discarded rx packet: "
" len %d, expected %zd\n", err, sock_len);
- vhost_discard_vq_desc(vq, headcount);
+ vhost_discard_vq_desc(vq, headcount, ndesc);
continue;
}
/* Supply virtio_net_hdr if VHOST_NET_F_VIRTIO_NET_HDR */
@@ -1252,7 +1263,7 @@ static void handle_rx(struct vhost_net *net)
copy_to_iter(&num_buffers, sizeof num_buffers,
&fixup) != sizeof num_buffers) {
vq_err(vq, "Failed num_buffers write");
- vhost_discard_vq_desc(vq, headcount);
+ vhost_discard_vq_desc(vq, headcount, ndesc);
goto out;
}
nvq->done_idx += headcount;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 8570fdf2e14a..b56568807588 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2792,18 +2792,11 @@ static int get_indirect(struct vhost_virtqueue *vq,
return 0;
}
-/* This looks in the virtqueue and for the first available buffer, and converts
- * it to an iovec for convenient access. Since descriptors consist of some
- * 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. A negative code is
- * returned on error. */
-int vhost_get_vq_desc(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)
+int vhost_get_vq_desc_n(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,
+ unsigned int *ndesc)
{
bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER);
struct vring_desc desc;
@@ -2921,16 +2914,40 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
vq->last_avail_idx++;
vq->next_avail_head += c;
+ if (ndesc)
+ *ndesc = c;
+
/* Assume notifications from guest are disabled at this point,
* if they aren't we would need to update avail_event index. */
BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY));
return head;
}
+EXPORT_SYMBOL_GPL(vhost_get_vq_desc_n);
+
+/* This looks in the virtqueue and for the first available buffer, and converts
+ * it to an iovec for convenient access. Since descriptors consist of some
+ * 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. A negative code is
+ * returned on error.
+ */
+int vhost_get_vq_desc(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)
+{
+ return vhost_get_vq_desc_n(vq, iov, iov_size, out_num, in_num,
+ log, log_num, NULL);
+}
EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
/* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
-void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n)
+void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n,
+ unsigned int ndesc)
{
+ vq->next_avail_head -= ndesc;
vq->last_avail_idx -= n;
}
EXPORT_SYMBOL_GPL(vhost_discard_vq_desc);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 621a6d9a8791..69a39540df3d 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -230,7 +230,14 @@ int vhost_get_vq_desc(struct vhost_virtqueue *,
struct iovec iov[], unsigned int iov_size,
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 n);
+
+int vhost_get_vq_desc_n(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,
+ unsigned int *ndesc);
+
+void vhost_discard_vq_desc(struct vhost_virtqueue *, int n, unsigned int ndesc);
bool vhost_vq_work_queue(struct vhost_virtqueue *vq, struct vhost_work *work);
bool vhost_vq_has_work(struct vhost_virtqueue *vq);
--
2.31.1
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