On Tue, Jul 18, 2023 at 09:02:35PM +0300, Arseniy Krasnov wrote:
> For non-linear skb use its pages from fragment array as buffers in
> virtio tx queue. These pages are already pinned by 'get_user_pages()'
> during such skb creation.
>
> Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
> Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> ---
> net/vmw_vsock/virtio_transport.c | 40 +++++++++++++++++++++++++++-----
> 1 file changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index e95df847176b..6cbb45bb12d2 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -100,7 +100,9 @@ virtio_transport_send_pkt_work(struct work_struct *work)
> vq = vsock->vqs[VSOCK_VQ_TX];
>
> for (;;) {
> - struct scatterlist hdr, buf, *sgs[2];
> + /* +1 is for packet header. */
> + struct scatterlist *sgs[MAX_SKB_FRAGS + 1];
> + struct scatterlist bufs[MAX_SKB_FRAGS + 1];
> int ret, in_sg = 0, out_sg = 0;
> struct sk_buff *skb;
> bool reply;
> @@ -111,12 +113,38 @@ virtio_transport_send_pkt_work(struct work_struct *work)
>
> virtio_transport_deliver_tap_pkt(skb);
> reply = virtio_vsock_skb_reply(skb);
> + sg_init_one(&bufs[out_sg], virtio_vsock_hdr(skb),
> + sizeof(*virtio_vsock_hdr(skb)));
> + sgs[out_sg] = &bufs[out_sg];
> + out_sg++;
> +
> + if (!skb_is_nonlinear(skb)) {
> + if (skb->len > 0) {
> + sg_init_one(&bufs[out_sg], skb->data, skb->len);
> + sgs[out_sg] = &bufs[out_sg];
> + out_sg++;
> + }
> + } else {
> + struct skb_shared_info *si;
> + int i;
> +
> + si = skb_shinfo(skb);
> +
> + for (i = 0; i < si->nr_frags; i++) {
> + skb_frag_t *skb_frag = &si->frags[i];
> + void *va = page_to_virt(skb_frag->bv_page);
>
> - sg_init_one(&hdr, virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb)));
> - sgs[out_sg++] = &hdr;
> - if (skb->len > 0) {
> - sg_init_one(&buf, skb->data, skb->len);
> - sgs[out_sg++] = &buf;
> + /* We will use 'page_to_virt()' for userspace page here,
don't put comments after code they refer to, please?
> + * because virtio layer will call 'virt_to_phys()' later
it will but not always. sometimes it's the dma mapping layer.
> + * to fill buffer descriptor. We don't touch memory at
> + * "virtual" address of this page.
you need to stick "the" in a bunch of places above.
> + */
> + sg_init_one(&bufs[out_sg],
> + va + skb_frag->bv_offset,
> + skb_frag->bv_len);
> + sgs[out_sg] = &bufs[out_sg];
> + out_sg++;
> + }
> }
>
> ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL);
There's a problem here: if there vq is small this will fail.
So you really should check free vq s/gs and switch to non-zcopy
if too small.
> --
> 2.25.1
