On 11/30/23 10:11, Lorenzo Bianconi wrote:
Similar to native xdp, do not always linearize the skb in
netif_receive_generic_xdp routine but create a non-linear xdp_buff to be
processed by the eBPF program. This allow to add multi-buffer support
for xdp running in generic mode.
Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
---
net/core/dev.c | 144 ++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 119 insertions(+), 25 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index 4df68d7f04a2..0d08e755bb7f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4853,6 +4853,12 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
xdp_init_buff(xdp, frame_sz, &rxqueue->xdp_rxq);
xdp_prepare_buff(xdp, hard_start, skb_headroom(skb) - mac_len,
skb_headlen(skb) + mac_len, true);
+ if (skb_is_nonlinear(skb)) {
+ skb_shinfo(skb)->xdp_frags_size = skb->data_len;
+ xdp_buff_set_frags_flag(xdp);
+ } else {
+ xdp_buff_clear_frags_flag(xdp);
+ }
orig_data_end = xdp->data_end;
orig_data = xdp->data;
@@ -4882,6 +4888,14 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
skb->len += off; /* positive on grow, negative on shrink */
}
+ /* XDP frag metadata (e.g. nr_frags) are updated in eBPF helpers
+ * (e.g. bpf_xdp_adjust_tail), we need to update data_len here.
+ */
+ if (xdp_buff_has_frags(xdp))
+ skb->data_len = skb_shinfo(skb)->xdp_frags_size;
+ else
+ skb->data_len = 0;
+
/* check if XDP changed eth hdr such SKB needs update */
eth = (struct ethhdr *)xdp->data;
if ((orig_eth_type != eth->h_proto) ||
@@ -4915,54 +4929,134 @@ u32 bpf_prog_run_generic_xdp(struct sk_buff *skb, struct xdp_buff *xdp,
return act;
}
-static u32 netif_receive_generic_xdp(struct sk_buff **pskb,
- struct xdp_buff *xdp,
- struct bpf_prog *xdp_prog)
+static int netif_skb_check_for_generic_xdp(struct sk_buff **pskb,
+ struct bpf_prog *prog)
I like this is split out into a check function.
{
struct sk_buff *skb = *pskb;
- u32 act = XDP_DROP;
-
- /* Reinjected packets coming from act_mirred or similar should
- * not get XDP generic processing.
- */
- if (skb_is_redirected(skb))
- return XDP_PASS;
(For other reviewers)
This reinjected check is moved further down.
+ int err;
- /* XDP packets must be linear and must have sufficient headroom
- * of XDP_PACKET_HEADROOM bytes. This is the guarantee that also
- * native XDP provides, thus we need to do it here as well.
+ /* XDP does not support fraglist so we need to linearize
+ * the skb.
*/
- if (skb_cloned(skb) || skb_is_nonlinear(skb) ||
- skb_headroom(skb) < XDP_PACKET_HEADROOM) {
+ if (skb_has_frag_list(skb) || !prog->aux->xdp_has_frags) {
int hroom = XDP_PACKET_HEADROOM - skb_headroom(skb);
int troom = skb->tail + skb->data_len - skb->end;
/* In case we have to go down the path and also linearize,
* then lets do the pskb_expand_head() work just once here.
*/
- if (pskb_expand_head(skb,
- hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0,
- troom > 0 ? troom + 128 : 0, GFP_ATOMIC))
- goto do_drop;
- if (skb_linearize(skb))
- goto do_drop;
+ err = pskb_expand_head(skb,
+ hroom > 0 ? ALIGN(hroom, NET_SKB_PAD) : 0,
+ troom > 0 ? troom + 128 : 0, GFP_ATOMIC);
+ if (err)
+ return err;
+
+ err = skb_linearize(skb);
+ if (err)
+ return err;
+
+ return 0;
+ }
+
+ /* XDP packets must have sufficient headroom of XDP_PACKET_HEADROOM
+ * bytes. This is the guarantee that also native XDP provides,
+ * thus we need to do it here as well.
+ */
+ if (skb_cloned(skb) || skb_shinfo(skb)->nr_frags ||
I though we could allow a SKB with skb_shinfo(skb)->nr_frags (that isn't
cloned or shared) to be processed by generic XDP without any reallocation?
So check would be: (skb_cloned(skb) || skb_shared(skb) ||)
+ skb_headroom(skb) < XDP_PACKET_HEADROOM) {
[Headroom trick]
For layered devices the netstack could be the process that created the
SKB. If you noticed my veth patchset[4/4], when I detect an XDP-prog
attach, I'm increasing the net_device headroom (.ndo_set_rx_headroom)
such that netstack will allocated enough headroom to satisfy
XDP_PACKET_HEADROOM.
[4/4]
https://lore.kernel.org/netdev/169272716651.1975370.10514711233878278884.stgit@firesoul/
+ u32 mac_len = skb->data - skb_mac_header(skb);
+ u32 size, len, max_head_size, off;
+ struct sk_buff *nskb;
+ int i, head_off;
+
+ __skb_push(skb, mac_len);
+ max_head_size = SKB_WITH_OVERHEAD(PAGE_SIZE -
+ XDP_PACKET_HEADROOM);
+ if (skb->len > max_head_size + MAX_SKB_FRAGS * PAGE_SIZE)
+ return -ENOMEM;
+
+ size = min_t(u32, skb->len, max_head_size);
+ nskb = netdev_alloc_skb(skb->dev, size + XDP_PACKET_HEADROOM);
Would is be possible to use napi_alloc_skb() here?
The napi_alloc_skb() is faster than netdev_alloc_skb(), but it as name
suggest assumes this is called under NAPI protection/context. It
used-to-be the case for generic XDP, but code got moved around to
support layered devices, so I not 100% sure if this is always true (NAPI
context).
+ if (!nskb)
+ return -ENOMEM;
+
+ skb_reserve(nskb, XDP_PACKET_HEADROOM);
+ skb_copy_header(nskb, skb);
+
+ err = skb_copy_bits(skb, 0, nskb->data, size);
+ if (err) {
+ consume_skb(nskb);
+ return err;
+ }
+ skb_put(nskb, size);
+
+ head_off = skb_headroom(nskb) - skb_headroom(skb);
+ skb_headers_offset_update(nskb, head_off);
+
+ off = size;
+ len = skb->len - off;
+ for (i = 0; i < MAX_SKB_FRAGS && off < skb->len; i++) {
+ struct page *page;
+ void *frag;
+
+ size = min_t(u32, len, PAGE_SIZE);
+ frag = netdev_alloc_frag(size);
Again the slower variant.
+ if (!frag) {
+ consume_skb(nskb);
+ return -ENOMEM;
+ }
+
+ page = virt_to_head_page(frag);
+ skb_add_rx_frag(nskb, i, page,
+ frag - page_address(page), size, size);
+ err = skb_copy_bits(skb, off, frag, size);
+ if (err) {
+ consume_skb(nskb);
+ return err;
+ }
+
+ len -= size;
+ off += size;
+ }
+
+ consume_skb(skb);
+ *pskb = nskb;
+ __skb_pull(nskb, mac_len);
}
- act = bpf_prog_run_generic_xdp(skb, xdp, xdp_prog);
+ return 0;
+}
+
+static u32 netif_receive_generic_xdp(struct sk_buff **pskb,
+ struct xdp_buff *xdp,
+ struct bpf_prog *xdp_prog)
+{
+ u32 act = XDP_DROP;
+
+ /* Reinjected packets coming from act_mirred or similar should
+ * not get XDP generic processing.
+ */
+ if (skb_is_redirected(*pskb))
+ return XDP_PASS;
+
+ if (netif_skb_check_for_generic_xdp(pskb, xdp_prog))
+ goto do_drop;
+
+ act = bpf_prog_run_generic_xdp(*pskb, xdp, xdp_prog);
switch (act) {
case XDP_REDIRECT:
case XDP_TX:
case XDP_PASS:
break;
default:
- bpf_warn_invalid_xdp_action(skb->dev, xdp_prog, act);
+ bpf_warn_invalid_xdp_action((*pskb)->dev, xdp_prog, act);
fallthrough;
case XDP_ABORTED:
- trace_xdp_exception(skb->dev, xdp_prog, act);
+ trace_xdp_exception((*pskb)->dev, xdp_prog, act);
fallthrough;
case XDP_DROP:
do_drop:
- kfree_skb(skb);
+ kfree_skb(*pskb);
break;
}
Overall I like the patch :-)
Are we missing more things to allow GRO packets getting processed by
generic XDP?
--Jesper
