Re: [PATCH v8 bpf-next 08/14] bpf: add multi-buff support to the bpf_xdp_adjust_tail() API
From: Vladimir Oltean <olteanv@gmail.com>
Date: 2021-04-08 19:16:04
Also in:
bpf
On Thu, Apr 08, 2021 at 02:51:00PM +0200, Lorenzo Bianconi wrote:
quoted hunk ↗ jump to hunk
From: Eelco Chaudron <echaudro@redhat.com> This change adds support for tail growing and shrinking for XDP multi-buff. Signed-off-by: Eelco Chaudron <echaudro@redhat.com> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org> --- include/net/xdp.h | 5 ++++ net/core/filter.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 68 insertions(+)diff --git a/include/net/xdp.h b/include/net/xdp.h index c8eb7cf4ebed..55751cf2badf 100644 --- a/include/net/xdp.h +++ b/include/net/xdp.h@@ -159,6 +159,11 @@ static inline void xdp_set_frag_size(skb_frag_t *frag, u32 size) frag->bv_len = size; } +static inline unsigned int xdp_get_frag_tailroom(const skb_frag_t *frag) +{ + return PAGE_SIZE - xdp_get_frag_size(frag) - xdp_get_frag_offset(frag); +} +
This is an interesting requirement. Must an XDP frame fragment be a full PAGE_SIZE? enetc does not fulfill it, and I suspect that none of the drivers with a "shared page" memory model will.
quoted hunk ↗ jump to hunk
struct xdp_frame { void *data; u16 len;diff --git a/net/core/filter.c b/net/core/filter.c index cae56d08a670..c4eb1392f88e 100644 --- a/net/core/filter.c +++ b/net/core/filter.c@@ -3855,11 +3855,74 @@ static const struct bpf_func_proto bpf_xdp_adjust_head_proto = { .arg2_type = ARG_ANYTHING, }; +static int bpf_xdp_mb_adjust_tail(struct xdp_buff *xdp, int offset) +{ + struct xdp_shared_info *xdp_sinfo = xdp_get_shared_info_from_buff(xdp); + + if (unlikely(xdp_sinfo->nr_frags == 0)) + return -EINVAL;
This function is called if xdp->mb is true, but we check whether nr_frags != 0? Is this condition possible?
+ if (offset >= 0) {
+ skb_frag_t *frag = &xdp_sinfo->frags[xdp_sinfo->nr_frags - 1];
+ int size;
+
+ if (unlikely(offset > xdp_get_frag_tailroom(frag)))
+ return -EINVAL;
+
+ size = xdp_get_frag_size(frag);
+ memset(xdp_get_frag_address(frag) + size, 0, offset);
+ xdp_set_frag_size(frag, size + offset);
+ xdp_sinfo->data_length += offset;
+ } else {
+ int i, frags_to_free = 0;
+
+ offset = abs(offset);
+
+ if (unlikely(offset > ((int)(xdp->data_end - xdp->data) +
+ xdp_sinfo->data_length -
+ ETH_HLEN)))I think code alignment should be to xdp->data_end, not to (int). Also: should we have some sort of helper for calculating the total length of an xdp_frame (head + frags)? Maybe it's just me, but I find it slightly confusing that xdp_sinfo->data_length does not account for everything.
+ return -EINVAL;
+
+ for (i = xdp_sinfo->nr_frags - 1; i >= 0 && offset > 0; i--) {
+ skb_frag_t *frag = &xdp_sinfo->frags[i];
+ int size = xdp_get_frag_size(frag);
+ int shrink = min_t(int, offset, size);
+
+ offset -= shrink;
+ if (likely(size - shrink > 0)) {
+ /* When updating the final fragment we have
+ * to adjust the data_length in line.
+ */
+ xdp_sinfo->data_length -= shrink;
+ xdp_set_frag_size(frag, size - shrink);
+ break;
+ }
+
+ /* When we free the fragments,
+ * xdp_return_frags_from_buff() will take care
+ * of updating the xdp share info data_length.s/xdp share info data_length/data_length from xdp_shared_info/
+ */
+ frags_to_free++;
+ }
+
+ if (unlikely(frags_to_free))
+ xdp_return_num_frags_from_buff(xdp, frags_to_free);
+
+ if (unlikely(offset > 0))
+ xdp->data_end -= offset;
+ }
+
+ return 0;
+}
+
BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
{
void *data_hard_end = xdp_data_hard_end(xdp); /* use xdp->frame_sz */
void *data_end = xdp->data_end + offset;
+ if (unlikely(xdp->mb))
+ return bpf_xdp_mb_adjust_tail(xdp, offset);
+
/* Notice that xdp_data_hard_end have reserved some tailroom */
if (unlikely(data_end > data_hard_end))
return -EINVAL;
--
2.30.2