vhost: vsock: add weight support [Linux 4.19.64]

This Linux kernel change "vhost: vsock: add weight support" is included in the Linux 4.19.64 release. This change is authored by Jason Wang <jasowang [at] redhat.com> on Fri May 17 00:29:51 2019 -0400. The commit for this change in Linux stable tree is 2399101 (patch) which is from upstream commit e79b431. The same Linux upstream change may have been applied to various maintained Linux releases and you can find all Linux releases containing changes from upstream e79b431.

vhost: vsock: add weight support

commit e79b431fb901ba1106670bcc80b9b617b25def7d upstream.

This patch will check the weight and exit the loop if we exceeds the
weight. This is useful for preventing vsock kthread from hogging cpu
which is guest triggerable. The weight can help to avoid starving the
request from on direction while another direction is being processed.

The value of weight is picked from vhost-net.

This addresses CVE-2019-3900.

Cc: Stefan Hajnoczi <stefanha@redhat.com>
Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

There are 16 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/vhost/vsock.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 58c5c82..bab495d 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -86,6 +86,7 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
                struct vhost_virtqueue *vq)
 {
    struct vhost_virtqueue *tx_vq = &vsock->vqs[VSOCK_VQ_TX];
+   int pkts = 0, total_len = 0;
    bool added = false;
    bool restart_tx = false;

@@ -97,7 +98,7 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
    /* Avoid further vmexits, we're already processing the virtqueue */
    vhost_disable_notify(&vsock->dev, vq);

-   for (;;) {
+   do {
        struct virtio_vsock_pkt *pkt;
        struct iov_iter iov_iter;
        unsigned out, in;
@@ -182,8 +183,9 @@ static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
         */
        virtio_transport_deliver_tap_pkt(pkt);

+       total_len += pkt->len;
        virtio_transport_free_pkt(pkt);
-   }
+   } while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));
    if (added)
        vhost_signal(&vsock->dev, vq);

@@ -358,7 +360,7 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
    struct vhost_vsock *vsock = container_of(vq->dev, struct vhost_vsock,
                         dev);
    struct virtio_vsock_pkt *pkt;
-   int head;
+   int head, pkts = 0, total_len = 0;
    unsigned int out, in;
    bool added = false;

@@ -368,7 +370,7 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
        goto out;

    vhost_disable_notify(&vsock->dev, vq);
-   for (;;) {
+   do {
        u32 len;

        if (!vhost_vsock_more_replies(vsock)) {
@@ -409,9 +411,11 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
        else
            virtio_transport_free_pkt(pkt);

-       vhost_add_used(vq, head, sizeof(pkt->hdr) + len);
+       len += sizeof(pkt->hdr);
+       vhost_add_used(vq, head, len);
+       total_len += len;
        added = true;
-   }
+   } while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));

 no_more_replies:
    if (added)

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