xsk: new descriptor addressing scheme

Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data.  Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).

By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.

In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.

In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.

We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.

To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.

On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.

Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.

This commit changes the uapi of AF_XDP sockets, and updates the
documentation.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 17 insertions, 13 deletions

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 966307ce4b8e..4688c750df1d 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -41,24 +41,27 @@ bool xsk_is_setup_for_bpf_map(struct xdp_sock *xs)
 
 static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
 {
-	u32 id, len = xdp->data_end - xdp->data;
+	u32 len = xdp->data_end - xdp->data;
 	void *buffer;
+	u64 addr;
 	int err;
 
 	if (xs->dev != xdp->rxq->dev || xs->queue_id != xdp->rxq->queue_index)
 		return -EINVAL;
 
-	if (!xskq_peek_id(xs->umem->fq, &id)) {
+	if (!xskq_peek_addr(xs->umem->fq, &addr) ||
+	    len > xs->umem->chunk_size_nohr) {
 		xs->rx_dropped++;
 		return -ENOSPC;
 	}
 
-	buffer = xdp_umem_get_data_with_headroom(xs->umem, id);
+	addr += xs->umem->headroom;
+
+	buffer = xdp_umem_get_data(xs->umem, addr);
 	memcpy(buffer, xdp->data, len);
-	err = xskq_produce_batch_desc(xs->rx, id, len,
-				      xs->umem->frame_headroom);
+	err = xskq_produce_batch_desc(xs->rx, addr, len);
 	if (!err)
-		xskq_discard_id(xs->umem->fq);
+		xskq_discard_addr(xs->umem->fq);
 	else
 		xs->rx_dropped++;
 
@@ -95,10 +98,10 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
 
 static void xsk_destruct_skb(struct sk_buff *skb)
 {
-	u32 id = (u32)(long)skb_shinfo(skb)->destructor_arg;
+	u64 addr = (u64)(long)skb_shinfo(skb)->destructor_arg;
 	struct xdp_sock *xs = xdp_sk(skb->sk);
 
-	WARN_ON_ONCE(xskq_produce_id(xs->umem->cq, id));
+	WARN_ON_ONCE(xskq_produce_addr(xs->umem->cq, addr));
 
 	sock_wfree(skb);
 }
@@ -123,14 +126,15 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
 
 	while (xskq_peek_desc(xs->tx, &desc)) {
 		char *buffer;
-		u32 id, len;
+		u64 addr;
+		u32 len;
 
 		if (max_batch-- == 0) {
 			err = -EAGAIN;
 			goto out;
 		}
 
-		if (xskq_reserve_id(xs->umem->cq)) {
+		if (xskq_reserve_addr(xs->umem->cq)) {
 			err = -EAGAIN;
 			goto out;
 		}
@@ -153,8 +157,8 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
 		}
 
 		skb_put(skb, len);
-		id = desc.idx;
-		buffer = xdp_umem_get_data(xs->umem, id) + desc.offset;
+		addr = desc.addr;
+		buffer = xdp_umem_get_data(xs->umem, addr);
 		err = skb_store_bits(skb, 0, buffer, len);
 		if (unlikely(err)) {
 			kfree_skb(skb);
@@ -164,7 +168,7 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
 		skb->dev = xs->dev;
 		skb->priority = sk->sk_priority;
 		skb->mark = sk->sk_mark;
-		skb_shinfo(skb)->destructor_arg = (void *)(long)id;
+		skb_shinfo(skb)->destructor_arg = (void *)(long)addr;
 		skb->destructor = xsk_destruct_skb;
 
 		err = dev_direct_xmit(skb, xs->queue_id);