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Subject[PATCH v4 1/5] vsock/virtio: limit the memory used per-socket
Date
Since virtio-vsock was introduced, the buffers filled by the host
and pushed to the guest using the vring, are directly queued in
a per-socket list. These buffers are preallocated by the guest
with a fixed size (4 KB).

The maximum amount of memory used by each socket should be
controlled by the credit mechanism.
The default credit available per-socket is 256 KB, but if we use
only 1 byte per packet, the guest can queue up to 262144 of 4 KB
buffers, using up to 1 GB of memory per-socket. In addition, the
guest will continue to fill the vring with new 4 KB free buffers
to avoid starvation of other sockets.

This patch mitigates this issue copying the payload of small
packets (< 128 bytes) into the buffer of last packet queued, in
order to avoid wasting memory.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
drivers/vhost/vsock.c | 2 +
include/linux/virtio_vsock.h | 1 +
net/vmw_vsock/virtio_transport.c | 1 +
net/vmw_vsock/virtio_transport_common.c | 60 +++++++++++++++++++++----
4 files changed, 55 insertions(+), 9 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 6a50e1d0529c..6c8390a2af52 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -329,6 +329,8 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
return NULL;
}

+ pkt->buf_len = pkt->len;
+
nbytes = copy_from_iter(pkt->buf, pkt->len, &iov_iter);
if (nbytes != pkt->len) {
vq_err(vq, "Expected %u byte payload, got %zu bytes\n",
diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index e223e2632edd..7d973903f52e 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -52,6 +52,7 @@ struct virtio_vsock_pkt {
/* socket refcnt not held, only use for cancellation */
struct vsock_sock *vsk;
void *buf;
+ u32 buf_len;
u32 len;
u32 off;
bool reply;
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 0815d1357861..082a30936690 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -307,6 +307,7 @@ static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
break;
}

+ pkt->buf_len = buf_len;
pkt->len = buf_len;

sg_init_one(&hdr, &pkt->hdr, sizeof(pkt->hdr));
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 6f1a8aff65c5..095221f94786 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -26,6 +26,9 @@
/* How long to wait for graceful shutdown of a connection */
#define VSOCK_CLOSE_TIMEOUT (8 * HZ)

+/* Threshold for detecting small packets to copy */
+#define GOOD_COPY_LEN 128
+
static const struct virtio_transport *virtio_transport_get_ops(void)
{
const struct vsock_transport *t = vsock_core_get_transport();
@@ -64,6 +67,9 @@ virtio_transport_alloc_pkt(struct virtio_vsock_pkt_info *info,
pkt->buf = kmalloc(len, GFP_KERNEL);
if (!pkt->buf)
goto out_pkt;
+
+ pkt->buf_len = len;
+
err = memcpy_from_msg(pkt->buf, info->msg, len);
if (err)
goto out;
@@ -841,24 +847,60 @@ virtio_transport_recv_connecting(struct sock *sk,
return err;
}

+static void
+virtio_transport_recv_enqueue(struct vsock_sock *vsk,
+ struct virtio_vsock_pkt *pkt)
+{
+ struct virtio_vsock_sock *vvs = vsk->trans;
+ bool free_pkt = false;
+
+ pkt->len = le32_to_cpu(pkt->hdr.len);
+ pkt->off = 0;
+
+ spin_lock_bh(&vvs->rx_lock);
+
+ virtio_transport_inc_rx_pkt(vvs, pkt);
+
+ /* Try to copy small packets into the buffer of last packet queued,
+ * to avoid wasting memory queueing the entire buffer with a small
+ * payload.
+ */
+ if (pkt->len <= GOOD_COPY_LEN && !list_empty(&vvs->rx_queue)) {
+ struct virtio_vsock_pkt *last_pkt;
+
+ last_pkt = list_last_entry(&vvs->rx_queue,
+ struct virtio_vsock_pkt, list);
+
+ /* If there is space in the last packet queued, we copy the
+ * new packet in its buffer.
+ */
+ if (pkt->len <= last_pkt->buf_len - last_pkt->len) {
+ memcpy(last_pkt->buf + last_pkt->len, pkt->buf,
+ pkt->len);
+ last_pkt->len += pkt->len;
+ free_pkt = true;
+ goto out;
+ }
+ }
+
+ list_add_tail(&pkt->list, &vvs->rx_queue);
+
+out:
+ spin_unlock_bh(&vvs->rx_lock);
+ if (free_pkt)
+ virtio_transport_free_pkt(pkt);
+}
+
static int
virtio_transport_recv_connected(struct sock *sk,
struct virtio_vsock_pkt *pkt)
{
struct vsock_sock *vsk = vsock_sk(sk);
- struct virtio_vsock_sock *vvs = vsk->trans;
int err = 0;

switch (le16_to_cpu(pkt->hdr.op)) {
case VIRTIO_VSOCK_OP_RW:
- pkt->len = le32_to_cpu(pkt->hdr.len);
- pkt->off = 0;
-
- spin_lock_bh(&vvs->rx_lock);
- virtio_transport_inc_rx_pkt(vvs, pkt);
- list_add_tail(&pkt->list, &vvs->rx_queue);
- spin_unlock_bh(&vvs->rx_lock);
-
+ virtio_transport_recv_enqueue(vsk, pkt);
sk->sk_data_ready(sk);
return err;
case VIRTIO_VSOCK_OP_CREDIT_UPDATE:
--
2.20.1
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