On Sun, Aug 27, 2023 at 11:54:34AM +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@xxxxxxxxxxxxxxxxx>
---
Changelog:
v2 -> v3:
* Comment about 'page_to_virt()' is updated. I don't remove R-b,
as this change is quiet small I guess.
v6 -> v7:
* Move arrays '*sgs' and 'bufs' to 'virtio_vsock' instead of being
local variables. This allows to save stack space in cases of too
big MAX_SKB_FRAGS.
* Add 'WARN_ON_ONCE()' for handling nonlinear skbs - it checks that
linear part of such skb contains only header.
* R-b tag removed due to updates above.
net/vmw_vsock/virtio_transport.c | 54 +++++++++++++++++++++++++++-----
1 file changed, 47 insertions(+), 7 deletions(-)
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index e95df847176b..8636477cf088 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -63,6 +63,10 @@ struct virtio_vsock {
u32 guest_cid;
bool seqpacket_allow;
+
I'd add a comment here specifying specifying what we need these fields
for and why we put them here (basically Paolo's suggestion).
+ /* +1 is for packet header. */
+ struct scatterlist *sgs[MAX_SKB_FRAGS + 1];
+ struct scatterlist bufs[MAX_SKB_FRAGS + 1];
};
static u32 virtio_transport_get_local_cid(void)
@@ -100,8 +104,9 @@ virtio_transport_send_pkt_work(struct work_struct *work)
vq = vsock->vqs[VSOCK_VQ_TX];
for (;;) {
- struct scatterlist hdr, buf, *sgs[2];
int ret, in_sg = 0, out_sg = 0;
+ struct scatterlist **sgs;
+ struct scatterlist *bufs;
struct sk_buff *skb;
bool reply;
@@ -111,12 +116,47 @@ virtio_transport_send_pkt_work(struct work_struct *work)
virtio_transport_deliver_tap_pkt(skb);
reply = virtio_vsock_skb_reply(skb);
-
- 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;
+ sgs = vsock->sgs;
+ bufs = vsock->bufs;
+ sg_init_one(&bufs[out_sg], virtio_vsock_hdr(skb),
+ sizeof(*virtio_vsock_hdr(skb)));
+ sgs[out_sg] = &bufs[out_sg];
IIUC `sgs[i]` always contains `&bufs[i]`.
Could we initialize it once when we allocate `struct virtio_vsock` in
`virtio_vsock_probe`?
Of course putting a comment in `struct virtio_vsock` about it.
Since we are using them only for out buffers, I'd also rename them in
out_sgs and out_bufs.
The rest LGTM.
Stefano
+ 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;
+
+ /* If skb is nonlinear, then its buffer must contain
+ * only header and nothing more. Data is stored in
+ * the fragged part.
+ */
+ WARN_ON_ONCE(skb_headroom(skb) != sizeof(*virtio_vsock_hdr(skb)));
+
+ si = skb_shinfo(skb);
+
+ for (i = 0; i < si->nr_frags; i++) {
+ skb_frag_t *skb_frag = &si->frags[i];
+ void *va;
+
+ /* We will use 'page_to_virt()' for the userspace page
+ * here, because virtio or dma-mapping layers will call
+ * 'virt_to_phys()' later to fill the buffer descriptor.
+ * We don't touch memory at "virtual" address of this page.
+ */
+ va = page_to_virt(skb_frag->bv_page);
+ 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);
--
2.25.1
