Commit 473c7391 authored by Stefano Garzarella's avatar Stefano Garzarella Committed by David S. Miller
Browse files

vsock/virtio: limit the memory used per-socket 



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.

Signed-off-by: default avatarStefano Garzarella <sgarzare@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d1a55841

drivers/vhost/vsock.c

+2 −0
Original line number Diff line number Diff line
@@ -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",

include/linux/virtio_vsock.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

net/vmw_vsock/virtio_transport.c

+1 −0
Original line number Diff line number Diff line
@@ -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));

net/vmw_vsock/virtio_transport_common.c

+51 −9
Original line number Diff line number Diff line
@@ -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 @@ destroy: 
	return err;

}



static int

virtio_transport_recv_connected(struct sock *sk,

static void

virtio_transport_recv_enqueue(struct vsock_sock *vsk,

			      struct virtio_vsock_pkt *pkt)

{

	struct vsock_sock *vsk = vsock_sk(sk);

	struct virtio_vsock_sock *vvs = vsk->trans;

	int err = 0;

	bool free_pkt = false;



	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);



	/* 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);

	int err = 0;



	switch (le16_to_cpu(pkt->hdr.op)) {

	case VIRTIO_VSOCK_OP_RW:

		virtio_transport_recv_enqueue(vsk, pkt);

		sk->sk_data_ready(sk);

		return err;

	case VIRTIO_VSOCK_OP_CREDIT_UPDATE:

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